Ralph will make you some nice floats here: http://www.geocities.com/planefunfloats/
Or you can order these which are also good, but a little less scale-looking http://users.cwnet.com/zdgreg/index.html

Length should be about 75% of your fuselage length. I estimate that to be 50 inches.

If you want "Scale" floats, look up "Sea Commander" floats. They are epoxyGlass, beautiful, expensive, and work very well.