From www.aomin.org:

Pastor David King provides the following example of an early church Father, a medieval Father, a Doctor of the Church (according to Rome), and a cardinal of the Roman church, all affirming imputation in some form or other.

Bernard of Clairvaux (1090-1153): The fragrance of your wisdom comes to us in what we hear, for if anyone needs wisdom let him ask of you and you will give it to him. It is well known that you give to all freely and ungrudgingly. As for your justice, so great is the fragrance it diffuses that you are called not only just but even justice itself, the justice that makes men just. Your power to make men just is measured by your generosity in forgiving. Therefore the man who through sorrow for sin hungers and thirsts for justice, let him trust in the One who changes the sinner into a just man, and, judged righteous in terms of faith alone, he will have peace with God. See Kilian Walsh, O.C.S.O., Bernard of Clairvaux On the Song of Songs II (Kalamazoo: Cistercian Publications, Inc.,1983), Sermon 22.8, p. 20.

Latin text: Porro sapientiae tuae odorem ex eo percipimus quod audivimus quia si quis indiget sapientia, postulet eam a te, et dabis ei. Aiunt siquidem quod des omnibus affluenter, et non improperes. At vero justitiae tuae tanta ubique fragrantia spargitur, ut non solum justus, sed etiam ipsa dicaris justitia, et justitia justificans. Tam validus denique es ad justificandum, quam multus ad ignoscendum. Quamobrem quisquis pro peccatis compunctus esurit et sitit justitiam, credat in te qui justificas impium, et solam justificatus per fidem, pacem habebit ad Deum. Sermones in Cantica, Sermo XXII, §8, PL 183:881D.

Bernard of Clairvaux (1090-1153): Man therefore was lawfully delivered up, but mercifully set free. Yet mercy was shown in such a way that a kind of justice was not lacking even in his liberation, since, as was most fitting for man s recovery, it was part of the mercy of the liberator to employ justice rather than power against man s enemy. For what could man, the slave of sin, fast bound by the devil, do of him self to recover that righteousness which he had formerly lost? Therefore he who lacked righteousness had another’s imputed to him, and in this way: The prince of this world came and found nothing in the Saviour, and because he notwithstanding laid hands on the Innocent he lost most justly those whom he held captive; since He who owed nothing to death, lawfully freed him who was subject to it, both from the debt of death, and the dominion of the devil, by accepting the injustice of death; for with what justice could that be exacted from man a second time? It was man who owed the debt, it was man who paid it. For if one, says S. Paul, died for all, then were all dead (2 Cor. v. 14), so that, as One bore the sins of all, the satisfaction of One is imputed to all. It is not that one forfeited, another satisfied; the Head and body is one, viz., Christ. The Head, therefore, satisfied for the members, Christ for His children, since, according to the Gospel of Paul, by which Peter’s [i.e., Abelard] falsehood is refuted, He who died for us, quickened us together with Himself, forgiving us all our trespasses, blotting out the hand writing of ordinances that was against us, and took it out of the way, nailing it to His cross, having spoiled principalities and powers (Col. ii. 13, 14). Dom. John Mabillon, ed., Life and Works of Saint Bernard, Abbot of Clairvaux, trans. Samuel J. Eales, Vol. II, Letter CXC – Against Certain Heads of Abaelard’s Heresies, 6.15 (London: Burns and Oates Limited, 1889), pp. 580-581. Cf. Epistola CXC, ad Innocentum II, Pontificem, Tractatus de erroribus Petri Abaelardi, Caput VI, §15, PL 182:1065B-D.

Robert Bellarmine (1542-1621): And in this way, it were not absurd, if any one should say that the righteousness and merits of Christ are imputed unto us, when they are given and applied unto us, as if we ourselves had satisfied God. For translation, see The Works of John Owen, The Doctrine of Justification by Faith, General Considerations, ed. William H. Goold, (Edinburgh: The Banner of Truth Trust, Third printing, 1977), vol. V, p. 56.

Latin text: Et hoc modo non esset absurdum, si quis diceret nobis imputari Christi justitiam et merita; cum nobis donentur et applicentur; ac si nos ipsi Deo satisfecissemus. Roberti Bellarmini, Opera Omnia, De Controversiis, Tomus Quartus, Pars Prima, De Justificatione (Neapoli: Apud Josephum Giuliano, 1858), Liber II, Caput 10, p. 523.

Bellarmine cannot deny this when he says that Christ can rightly be said to be made righteousness meritoriously “because he satisfied the Father for us, and gives and communicates that satisfaction to us, when he justifies us, so that he can be called our sanctification and righteousness, as if we ourselves had satisfied God” (“De Justificatione,” 2.10 Opera [1858], 4:523). This he confirms on 2 Cor. 5:21: “The righteousness of Christ is imputed to us as to the satisfaction, which he made for us” (ibid., p. 524). Nor can that which our opponent adds in the same place help his cause when he says: “But not on this account can we be reckoned righteous, if the stains and corruption of sins truly inhere in us” (ibid.). For if the righteousness of Christ is imputed to us (as he had already confessed), then certainly we are considered righteous in him; for no one imputes righteousness to him whom he does not count righteous. And if the satisfaction of Christ is imputed to us, then our debts for which he satisfied are not imputed [to us], but are remitted. Falsely also he holds “that the righteousness inhering in us is here called the righteousness of God because it is given to us of God; or also because it is the image and effect of the righteousness of God” (ibid.). For the little clause “in him” stands in the way; for how could it be said to be in Christ, if it was in us? [Cardinal] Contarini acknowledges this: “The righteousness of God in him, since his righteousness is made ours, is given and imputed to us” (cf. “De Justificatione,” Casparis Contareni Cardinalis Opera [1571], p. 592).

Francis Turretin, Institutes of Elenctic Theology, Vol. 2, pp. 652-53, Sixteenth Topic, Third Question, Section XVII, (Phillipsburg, NJ: P&R Publishing, 1994)

Theodoret of Cyrrhus (393-466) commenting on Psalm 22:1: Let it [i.e., the LXX] therefore heed John’s loud cry, “Behold the Lamb of God, who takes away the sin of the world,” and the divinely inspired Paul’s words, “For us he made him to be sin who did not know sin so that we might become righteousness through him,” and again, “Christ redeemed us from the curse of the Law by becoming a curse for us.” So just as the one who was a fount of righteousness assumed our sin, and the one who was an ocean of blessing accepted a curse lying upon us, and scorning shame endured a cross, so too he uttered the words on our behalf. After all, if he willingly submitted to chastisement prescribed for us—“Chastisement of our peace is upon him,” the inspired author says—much more is it the case that it was on our behalf that he employed these words in our person, crying out, The words of my failings are far from saving me: do not have regard to the faults of nature, he is saying, but grant salvation in view of my sufferings. Robert C. Hill, The Fathers of the Church, Vol. 101, Theodoret of Cyrus, Commentary on the Psalms, 1-72 (Washington D.C.: The Catholic University of America Press, 2000), pp. 146-147.

Greek text: ??????????? ?????? ??????? ??? ???? ???????· «??? ? ????? ??? ????, ? ????? ??? ???????? ??? ??????.» ??? ?? ????????? ?????? ????????·«??? ?? ?????? ???????? ???? ???? ???????? ????????, ??? ????? ???????? ?????????? ?? ????.» ??? ?????· «??????? ???? ?????????? ?? ??? ???? ??? ????????, ????????? ???? ???? ??????.» ????????? ????? ??????????? ??????? ????, ??? ???????? ???????? ???????, ??? ???????? ?? ???? ???, ??? ??????????????? ??????? ???????, ??? ??????? ????????? ???????? ????????????· ???? ??? ???? ???? ???? ????????? ??????. ?? ??? ??? ????????? ???? ???????? ???????????· «??????? ??? ??????? ???? ??? ?????,» ? ????? ? ????????· ????? ?????? ???? ???? ???? ???? ???? ???????? ??????, ??? ??? «?????? ??? ??????????? ??? ?? ????? ??? ???????????? ???.» ?? ?????????, ?????, ??? ?? ??? ?????? ????????????· ???? ??? ??? ???????? ??? ?? ??? ????????. Interpretatio in Psalmos, Psalmi XXI, v. 1, PG 80:1012.

Addendum, thanks to Bruce McCormack’s Justification in Perspective:

Ambrosiaster (fl. 4th century): This he says, that without the works of the law, to an impious person (that is, a Gentile) believing in Christ, his faith is imputed for righteousness, as it was to Abraham. How then can the Jews imagine that through the works of the law they are justified with Abraham’s justification, when they see that Abraham was justified not from the works of the law, but by faith alone? Therefore there is no need of the law, since an impious person is justified with God through faith alone. Ambrosiaster, Commentary on Paul’s Epistles, on Romans 4:5 (PL 17:86).

Tertullian (c. 160 – c. 225): In short, faith in one of two gods cannot possibly admit us to the dispensation of the other, so that it should impute righteousness to those who believe in him, and make the just live through him, and declare the Gentiles to be his children through faith. Such a dispensation as this belongs wholly to Him through whose appointment it was already made known by the call of this self-same Abraham, as is conclusively shown by the natural meaning. Tertullian, Against Marcion, Book 5, Chapter 3