Haha, David, cloudberry resides in swamps and northern finland..and they are, as are all berries and 'shrooms, available in our forests and swamps to anyone who want's to go and pick them! But since my prospected gardens in archipelago of Finland usually don't have and swamps...

. Then again, it's all about testing in permaculture, right? Even though all info says that growing cloudberry in a large scale has proven very difficult, and that all our cloudberry crops are harvested from natural habitats, that doesn't mean that I should not try

!
Same goes for chestnuts, as Dirk suggested. We have tried to grow chestnuts in Finland about two hundred years without significant success..but climate change, microclimates and so on, I guess I should try! But rather than buy several small chestnuttrees, and see them destroyed in first winter, I'd rather just plant millions and millions of nuts, and see which one survives. Now where to get such amounts of valid seeds, I do not know
Plums are usually quite well adapted here, so I might just craft some of that mirabelle to any of our "wild" damson plums that grow like weeds around our garden.
I will see if I'm able to find that Fernor-walnut somewhere in europe to sell. Also I will continue to observe all these different other walnut trees, maybe they do actually make full nuts after all! And to say that city climate is warmer than countryside...true, but these trees that I observe are not surrounded by any buildings by a longshot, they are away from urban centers. And really, Finland does not HAVE a really big city anywhere

. Also while I'm talking about climate, the sea equalises spring weather somewhat, so even if days would be suprisingly warm the cold wind from sea would balance that. Average temp.in march-may was 2013 3.5C , and 2016 6,5C. That's entire average from three months, in may we had over 20C. I guess there are potential for late freezes, but I don't remember any big ones.
I have already planted few quinces, and have seeds for many more, going to sow them this fall. I expect them to fully reach their potential here, so it's marmelade ahoy!
So any hints where to order black mulberries? And to Dirk I would ask: in what type of soil does your paw paws live? They are by far my number once concern now, and after I plant them to the ground, I'm gonna shade them a bit, and build a mighty fortress around them, and wage war on rabbits during the winter.
I appreciate all answers already, this was my first post to these boards, nice to see that there are people that actually answer! I wish that I could help someone somewhere and send some seeds or plants or whatever...but it seems that here in the north it is WE who want all kinds of things from the south, hehe.
-Janne