With all this in mind the question remains: Why is the rest of the world silent?
To me, radio raises less of a question than other factors. Radio as we've seen doesn't work anymore, without exceptional magical aid. Everything we know about life in the rash era supports this, including the fact that the Finnish lake communities can only learn each others' fates from passing travelers. (It's possible that radio within cleared areas starts to work again, and while that would be of course helpful it doesn't help with communicating between areas.)
For me the big question is ocean travel. We've seen that islands fare better than connected areas when it comes to survival. That should mean that, in general, coasts are a likely place to find survivors, and also the easiest to assess and reach from the sea. So if Iceland has the resources to establish regional trade in a serious way, which we've seen that they do, they certainly have the means to attempt long-duration contact expeditions to likely survival areas -- Greenland, the Azores, the Canaries, the Mediterranean, even the Canadian maritimes are all within roughly the same range as Finland and Sweden, and half the world is within range of a deep water expedition with only 2-3 times the endurance of a trade run between Reykjavík and Keuruu.
I guess my point is, even without radio, they can still just go there and ask. Knock, knock! "Hey! Hellooo! Anyone home?"
So. What's stopping them? Is it cultural taboo? Or does something bad happen to every mission they attempt?