It is a hard thing to find. The soles have to be flat without raised cushion bumps or crazy designs. I use a 75% worn out cross training type shoe sole for max stiffness and flatness. You could always take a belt sander to it if you don't want to wait around for it to go flat. Then get a wide platform pedal used for bmx that's flat and no concave. This will eliminate any shoe squish or bounce and be rock solid at 500-600 watts.