You're not going to find too many true to style hefeweizens in the states. Most breweries make an American Wheat though it sounds like this isn't what you're looking for.
Personally, almost all of the beers I brew are some form of American wheat. My favorites being my Heather Wheat and my IPW (India Pale Wheat
If you haven't tried it yet I suggest the UFO from Harpoon
here in Boston. I don't think it'll be exactly what you're looking for though because it is an American Wheat.
edit: my '71 Sportster is in the garage just waiting for the sun for a kick-start.