Sorry for late reply, but I had to ask from Ahti as I'm not willing to give my own away.
We came into conclution that you can get one (with Skandinavian keyboard & BIOS) for 20€ if you come to pick it up from the party. If you take also a Swedish MSX friend with you, you can get it for free.
We have tried to get some contacts to Sweden as well because we know that there was huge amount of Spectravideo users back in the 80'ies. Somehow it just seems quite hard... propably because I don't know where to look and my Swedish skills sucks. According to my knowledge I think that you should be able to get one easyly by just placing "want to buy" adverticement in local paper, but I might be wrong.
About the party... Unfortunately the date is not yet set as it depends of when we can get the party place, but the party will be a weekend in summer or early autumn.