Boy, you'd have to do some research. The aftermarket does have wheels, but not many for civil aircraft, or smaller aircraft. The only thing I can think of is to find wheels for a larger aircraft in 1:72. You'd have to research a bunch of bombers, find gear diameters and compare with Cessna tire size in 1:48. I assume the kit gear legs could be reasonably modified to take new wheels. Another possibility would be to use the wheels from another kit, like their new 1:72 which has seperate wheels and pants.
Brings up a wish for Minicraft. Their new 172 kit is a gem- new level of detail for a Minicraft 1:48 civil subject, excellent quality molding. I sure wish they'd modify (or even completely redo) their older kits like the 140 and Cherokee. Also wish they'd do some of the older civil aircraft (like Stinsons and Beech).