There are probably a jillion r/c rubber tire sizes and tread designs out there, and I'm sure some would come close to what would work for this model. Then there's the cost and shipping of eight tires. I think maybe the age old problem of finding proper track for a tank project is easier than finding tires.
Hmmmm ....... that gives me an idea ......... here's Mato Pz III track without having to modify the lower hull. Wider track might mean a lower hull rebuild, but why not??? Another idea ----- build a lower boat hull and turn this LAV into a PBR !!!

I've done sillier things when I forgot to take my medication LOL

rex