Is there a Church Father or Doctor of the Church who wrote that Judas Iscariot was saved?

Not that I know of, but St. Thomas Aquinas writes that St. Peter is saved and Judas is not (Super Sent. lib. 4 d. 46 q. 1 a. 2 qc. 2 ad 3):

To damn Peter, to whom salvation is due by the favor of the grace conferred on him, would be contrary to justice; and so God cannot do this, speaking of his ordinary power. But to save Judas would not be contrary to justice, but above and beyond it, as is clear from what has been said. But nevertheless it would be contrary to his foreknowledge and disposition, by which he prepared for him an eternal punishment. Therefore, the order of justice does not prevent him from saving Judas, but the order of foreknowledge and eternal disposition prevents it.
_{damnare Petrum, cui ex beneficio gratiæ sibi collatæ salus debetur, esset contrarium justitiæ; unde hoc Deus non potest, loquendo de potentia ordinaria. Sed salvare Judam non esset justitiæ contrarium, sed præter eam, ut patet ex dictis; sed tamen esset contrarium ejus præscientiæ et dispositioni, qua ei æternam pœnam paravit; unde justitiæ ordo non impedit quin posset salvare Judam; sed impedit ordo præscientiæ et dispositionis æternæ.}

Christ forgave those who crucified him, and he would definitely have forgiven Judas. It is we Christians who find it impossible to see Judas forgiven ! Tell me : which is the commandment Judas broke by betraying Jesus ? If it is the one on killing, we have numberless people who killed more, including their hapless unborn children ! He might have foolishly belived that Jesus would easily escape from the Jews as he had done earlier. So, his mistake was not that he betrayed his master, but that he took the decision of ending his life all by himself. Remember that the Church traditionally condemned those members who would commit suicide. In some places their bodies were buried out of the normal boundaries of the cemetary in a place called the Rogue Pit. Things have since changed, with compassion and research on psychology gaining the upper hand. Patience, and we may have many surprises on the Final Judgement Day . ( Sorry,these are only some stray thoughts and not a direct answer to the question. I would rather put them in Comments column but for the space constraint . )

No Church Fathers or early reputable sources that I am aware of.

The most prominent ancient text which considers Judas Iscariot a hero is the Gnostic Gospel of Judas. It was not written by Judas--it appears to date to the 2nd century, long after Judas Iscariot was dead.

A polite description of The Gospel of Judas would be that it is pseudepigraphal. A more blunt description would be that it is a forgery. There is no basis for concluding that it is a reliable historical document; it's origin is far more likely a creation of 2nd-century Gnostic propaganda.

The Gospel of Judas claims that Judas was the sole disciple faithful enough to receive greater teachings from Jesus and to carry out the dreadful but necessary mission of handing Jesus over to the authorities. This view of Judas gained some attention when the a copy of the long-lost Gospel of Judas was rediscovered in the 20th century.

Prior to the rediscovery of the Gospel of Judas, there had been some periodic efforts in the last few centuries to recast Judas as a hero; I am unaware of any ancient basis for these views.

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The Evidence of Early, Well-Placed Sources

If we accept the traditional authorship of the 1st & 4th Gospels (I do, see my thoughts here & here), then we have two very relevant early documents written by people who were there and knew Judas personally.

Matthew states:

The Son of man goeth as it is written of him: but woe unto that man by whom the Son of man is betrayed! It had been good for that man if he had not been born (Matthew 26:24).

And John quotes Jesus referring to Judas thus:

none of them is lost, but the son of perdition (John 17:12)

Matthew & John were in a pretty good position to know what they were talking about, and they do not cast Judas in a positive light. They do not appear to believe Judas in on-track for salvation.