Church father Chromatius, writing around the turn of the 4th century, appeals to an interesting OT example to defend the perpetual virginity of Mary:
Remember that Miriam the prophetess of the Old Testament (the sister of Moses and Aaron) remained a virgin unsullied by man, having beheld the light of heavenly signs after the plagues of Egypt and the parting of the Red Sea and the Lord's glory going in advance and seen in a pillar of fire and clouds. It is not plausible therefore that the Mary of the Gospel, a virgin bearing God, who beheld God's glory not in a cloud but was worthy of carrying him in her virginal womb, had relations with a man. (source)
I reviewed the Wikipedia article on Miriam, and it seems to indicate that Chromatius's understanding is contrary to that of Judaism – the article mentions the Midrash as saying that Miriam had a spouse. Furthermore, Chromatius seems to make much of Miriam's status as a "prophetess," yet many prophets had spouses (e.g., Moses, Isaiah, Hosea)
So I wonder – what is the origin of this tradition, that Miriam was a virgin? Did it develop in association with the doctrine of the perpetual virginity of Mary, or was Chromatius relying on an older tradition?