The problem is that the ECF do not mention Penal Substitution Theory. They mention passages and biblical ideas that others articulated into Penal Substitution Theory. Those ideas are true. Those passages are true. It is what Penal Substitution Theory does with those passages that sets the theory apart from other theories.
The problem in this area is simply poor scholarship. Some (some who should know better) extract comments from earlier writings and provide a new context to the authors in order to "prove" a false conclusion.
For example, some will look at the fact that Christ bore our sins in His flesh, suffered and died for us, took upon Himself the wrath that was due man, and died on our behalf as a proof that Penal Substitution Theory was a well known doctrine. But this is reading into the text. What the ECF's do with those biblical truths is what demonstrates they did not hold to the theory you advocate (e.g., Origen with his payment to Satan; Martyr's focus on the physical death and it's implications to the human race; Irenaeus Recapitulation view....even William Tyndale's scapegoat theory).
The theory which we call Penal Substitution Theory does not only hold that Christ died for us so that we would escape the wrath that is to come. It holds that divine justice is retributive, that on the cross the Father was wrathfully punishing Jesus in our place as being guilty for our sins. This part (which is critical to the Penal Substitution Theory of Atonement (PSA) is not present in anything we know of prior to the Reformation. PSA is Thomas Aquinas' theory of atonement reformed.
As a grad student this was one of my passions. Studying the works of the ECF's is interesting and rewarding. But we should never try to conform early works to our own agenda. They reflect the thoughts, worldview, and ideologies contemporary to their world. I can't stand when people get inventive with history.
Once you understand this you can appreciate the value of historic theology and can see not only how each generation addressed its own issues but also how some doctrines developed and were influenced by others.