as has been said, realistic WWII model guns, unfortunately, would look way too puny, even in the hands of grots...ork shootas are bloody huge! - about the same size as a space marine heavy bolter!
a little pricey, but I'd say by far your best bet for something like this would be
Kromlech ...they'll have pretty much anything you'd want for a WWII-style ork army...couple of example pics...
they do full squads:
or if you just want guns: