Unfortunately the only way to avoid unbalanced leagues is to load every single league in the game, which obviously isn't possible or practical.
I try to run as many leagues as I can in and around the area I want to manage in. I'm fortunate I can get away with a lot of leagues nowadays, but when I ran a save in Portugal I just loaded Spain, said Portupoofs and Brazil.
My cuurent save has the whole of Europe loaded and oddly there seems to be a huge amout of Greek and Greek Cypriot talent available, with next to no decent Nordic players. I think it's just the way it goes.
At the end of the day you can only play what you've got in front of you (/football cliches) and to me if that means I can only sign Belgians while managing in Holland then that's what I do. After all it's only a game, it's not real. I think.