Didnt you just say that p. schiedeana can survive -12C and be fine, you wrote that in one of the above comments, or did I misunderstand it?
Not exactly.
In the Avocado genus Persea, "none of the species are very tolerant of severe winter cold, with the hardiest, P. borbonia, P. ichangensis and P. lingue,
surviving temperatures down to about −12 °C (10.4 °F) "
The hardiest, P. borbonia, P. ichangensis and P. lingue, none are in the same sub group as Avocado.
Only Persea schiedeana, the Coyo is in the same group, along with Avocado sub species.
So the hardiest, Persea, ( P. borbonia, P. ichangensis and P. lingo,) can survive temperatures down to about −12 °C (10.4 °F)
However they are not so closely related to Avocado, only the P. schiedeana is a direct relative compatible for X breeding and grafting easily.
P. schiedeana is said to be on the cold tolerant end of the Avocados. It also has highland forms, from cooler upland forests, which may be at the better end on that.
If it could survive such low temperatures as -12 ' C it would be widely grown already.
Sorry for the confusion. I was hoping that a USA member could answer your question about where seed can be found.