[Edi]

The list of heroes in the DB is most definitely not complete in the nations section, but if you look up the various heroes in the AllUnits tab, it more often than not lists the nations that have them. However, that's not complete either.

I think Xietor had done a fairly thorough listing of which nation got what when he was working on his Throne of Heroes mod.

I can try to complete the DB heroes listing, but if someone else already has a full list, I'd prefer that option, since there's not a whole lot of else that needs doing on the DB.