Summarizing Hanson’s “500 years of Early Christian Universalism” is on my list of things to do. I know he eventually mentions what the six schools were, and why he regards four as teaching universalism, but he does so in a very piecemeal fashion. Also, he doesn’t bother to mention the names of the two other schools, just where they basically were! (And he denies they were proper seminaries. 
)
The two main schools were Alexandria (in Egypt) and Antioch (in Asia Minor); each one had a related school, one in Caesarea (the port of northwestern Palestine–there were lots of Caesarea-es ) from Alexandria, and one in Syria somewhere (Damascus or Taursus if I recall correctly) from Antioch. (Edited to add: the school was certainly moved eventually to Nisibius, outside the Roman Empire, where it functioned as the most advanced medical university in the West, perhaps the world, well into the Muslim era.) The Syrian school eventually became the base of operations for the Church of the East after the orthodox party sacrificed Nestorius as an example involving too much schism in the two natures of Christ (even though he went to the grave denying this and insisting instead that he agreed with Pope Leo on the topic–or rather that Pope Leo agreed with him! )
Another Asia Minor school featured many annihilationists; and then the North African school (in Tunisia or Cyrenia), which was highly connected to Latin Rome, featured many ECTists (most prominently Augustine.)
Hanson’s argument that the four schools “taught” universalism is rather loose, and has come under rightful criticism in the century+ since publication; but I think he makes a decent case for a prevalence of universalism in the four schools, especially among their top masters.
We know from Augustine that there were many universalists around, however, that’s quite different from it being taught officially. I’d love to hear if you have any luck finding proof, one way or the other.