Hi, I am Sune from Denmark, and I have had the same idea as you for some time. Such seeds are very hard to get, but of all the things that I would like to grow in our garden - avocado ranks very high. Actually, you could try to contact the profile from this forum: tiendadefruta, Manolo Mateos. Not very active in here. He is from Spain and not long ago he gave me his phone number - you could try: +34 649 881 601. He might have cold hardy types. I have not had time to contact him, but it might be the best chance. Maybe it would even be possible with grafted plants - I don't know. You can send plants within EU.
A guy in UK runs a Youtube channel called Go Tropical UK. Unfortunately his is not very active anymore. But he got some cold hardy avocado seeds from US. He gave me the name of his supplier and I tried to contact him - but in vain. He never answered. Anyway, it has become very difficult to get seeds from US. I bought seeds from Trade Wind Fruits many times, but it is not possible anymore.
Would be nice to hear about you project. And if I find time, I will also still try to plant avocados. I would prefer grafted plants, as it takes a very long time from seed to fruit, as you may know.
We have had a couple of cold winters here in Denmark, and I am not sure that avocados would actually survive. I have killed a white sapote and what was supposed to be a very cold hardy lemon - but some stuff will survive... and I do use winter protection for the young plants. Best regards Sune