Let me make a few observations on assertions that Early Church Fathers were pretribulational.
Shepherd of Hermas: Yet it also says that "Happy ye who endure the great tribulation that is coming on, and happy they who shall not deny their own life." and "Those, therefore, who continue steadfast, and are put through the fire, will be purified by means of it. For as gold casts away its dross, so also will ye cast away all sadness and straitness, and will be made pure so as to fit into the building of the tower. … Wherefore cease not speaking these things into the ears of the saints. This then is the type of the great tribulation that is to come."
Cyprian: This is a most egregious ripping a text out of context. Please read the entire piece. Cyprian is encouraging Christians who are in the midst of a plague not to fear death. For the earlier departure in the quotation is exactly that.
"Many of our people die in this mortality, that is, many of our people are liberated from this world. This mortality, as it is a plague to Jews and Gentiles, and enemies of Christ, so it is a departure to salvation to God's servants. The fact that, without any difference made between one and another, the righteous die as well as the unrighteous, is no reason for you to suppose that it is a common death for the good and evil alike. The righteous are called to their place of refreshing, the unrighteous are snatched away to punishment; safety is the more speedily given to the faithful, penalty to the unbelieving. We are thoughtless and ungrateful, beloved brethren, for the divine benefits, and do not acknowledge what is conferred upon us. Lo, virgins depart in peace, safe with their glory, not fearing the threats of the coming Antichrist, and his corruptions and his brothels. Boys escape the peril of their unstable age, and in happiness attain the reward of continence and innocence. Now the delicate matron does not fear the tortures; for she has escaped by a rapid death the fear of persecution, and the hands and the torments of the executioner. By the dread of the mortality and of the time the lukewarm are inflamed, the slack are nerved up, the slothful are stimulated, the deserters are compelled to return, the heathens are constrained to believe, the ancient congregation of the faithful is called to rest, the new and abundant army is gathered to the battle with a braver vigour, to fight without fear of death when the battle shall come, because it comes to the warfare in the time of the mortality."
Justin Martyr: This is a pretty weak reed upon which to base a case of pretribulationism. Read the rest of the apology and tell me with a straight face that Justin is advocating such a view.
Iraeneus: This would appear to be the best of the lot, except that postmillenialists also claim Iraeneus because they convincingly argue that the the church's being "caught away" is at the end of the tribulation; otherwise, how can this be the "last contest of the righteous"?