I got my modern day 22.5" tubeless wheels that won't make my wife a widow at random like the FR5s the bus came with, from here.. https://buytruckwheels.com/products/22-5x6-75-white-steel-10x8-75-old-chevy-2-ton-trucks

It's a buy once, cry once deal-$60 apiece more than when I bought them, because "winning bigly," however as far as I know, they're the only game in town for these wheels. They're well made and DOT certified, but they're essentially semi tractor rims, which means the metal flange is 3/64" thicker than the originals. You might well need longer lug nuts, as 6/64" is 3/32" which is too much recess into the lugnuts for safety.

There's a thread about this where another 'Bolter had some longer lug studs made, he might chime in here also.

1965 C60 school bus | 1967 GMC 6500 school bus