Just stumbled on this small cie here in Quebec. They have a good range of nut trees and also seeds for sale. They sale also rare and indigenious trees for our area and others. They seems to ship internationaly but didn't read the infos yet. But the prices seems really good (at least for canadian folks).
Hope it will help. I think I will buy a couple of trees for here, zone 4 a-b (nobody seems to agree where we are).