unfortunately I can't find the seller on Ali Exp I bought the truck tyres from, but they are 75mm diam x 45mm wide. There are numerous types of tyres for sale from different sellers, takes a bit of searching to find what you need. The through drive diffs I used, the front axle and the gear motor I used are pictured. The wheels you buy may need the appropriate hex drive nuts.
Lews' idea re the 6x6 truck models you may be able to convert, as you can get everything you need in one model, although some can be expensive. Cheaper ones (around NZ $100) are usually just toys, and small scale (1/32 1/24) with plastic bits.
Took me a lot of looking to find all the bits I wanted, and some of the sellers don't exist any more. You find something good, and go back 6 months later to buy more, and they've gone.
The parts pictured are still available (1/10 scale) but if you want 6x6, you will need the front diff instead of the axle like mine has. Hard to find a proper differential, as most are not differentials, just drive axles, (as mine are) and make steering difficult, (want to go straight). The 'diffs' I'm using are very robust with solid components, - mine are completely packed with grease and pressurised, (my mod)
You could go another way with internal drives and axles with seals with arms outside for support, and using a gear motor for each side (mixed with steering) to give a differential action, but you still need a front diff. Lots to think about, but a fun project.😁