I mentioned on an earlier post a few good places to find belts for belt sanders that are much more suitable for knife grinding/sharpening.
Most of the 100, 150 and 220 grit belts are aluminum oxide and geared towards woodworking.
Knife-maker vendors are the best sources for a large selection of quality belts and belts geared towards working with hardened steel.
Lee Valley Belts Jantz Knife SupplyTexas Knife Supply - Sanding BeltsPop's Knife Supply - Sanding Belts I think it was Snotpig who had good luck with the premium belts from here:
McMaster-Carr - Sanding belts