I have amassed 6 or so pairs of 8" Tornado wheels off disposed rusted out chassis in decent shape, but you're not wrong about the caps. I only have one uniform set of undamaged caps including the wheels on two complete Tornado mowers. All have ball bearings though with two main tread designs from memory.
One solution is to fit a different pair each side or turn a disc of PVC and screw them on with a pair of screws.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!