Is it so that if you give two weapons to a unit (s)he automatically uses both? If that is the case then here's the nation dedicated to dual-wielding. =) It's just that I've been under impression that in ancient Japan using two swords (long ones, at least) was considered somewhat barbaric. Samurais had katana and short sword, but they weren't used at the same time. Therefore Japan as the nation of dual-wielders strikes me as 'unthematic' (not that it has any relevance to a fantasy setting), but I might very well be wrong. (Of course, for ninjas and ronins everything goes, it's just those samurais with twin katanas...)
While still on that subject, there's this historical figure whose fame was partially owed to the fact he used two swords
, Miamoto or something, to succesfully beat a heap of people. Good enough for a hero?