Hi,
I believe the GWS floats fit the Super Cub. You may need to do a bit of research on how to fit them because I don't think they are a direct fit, but they do work. Tower Hobbies has them, and they're cheap! http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHCR6&P=SM If you do it, post a photo! ;-)
Alternatively there are a couple of foam RTF float planes from Icon RC. I don't know how they are, but they look like fun!