Ante-Nicene Fathers Volume VI
Gregory Thaumaturgus: Part II: Dubious or Spurious Writings: Four Homilies
The emphasis in these homilies on the annunciation to Mary of her pregnancy on Mary's person shows that these are much, much later ("after Nicea... probably after Ephesus" as the Elucidation says). And while they're useful enough for showing our Catholic friends that there is absolutely no idea of a perfect Mary, and that even in speaking about Mary the later early church still held Christ alone to be the source of salvation, I don't know that these are necessarily all that useful for spiritual edification. The Fourth Homily is worth skimming, but you can reasonably skip the rest.