Did you consider Du-Bro 1/5 scale vintage wheels? They are 5.6" diameter (bit bigger than the H9 5.4" or so) and they are for 3/16" axles. A bit closer in diameter and axle.
It says the tires are foam, but it looks like it's coated to be slick.
http://www.shopatron.com/products/pr...560V/101.0.1.1