Most of the workhorse parts are off the rack at your local Chevy dealer, HOWEVER not all, the fuel filter for example is no longer made.. That said there is an easily obtained adapter to use a standard GM filter on the unit. And that's how it goes.
As for tires, 22.5's are used on Gassers as well.. I should know, I'm siting on six of 'em and this sucker sucks gasoline.
One nice thing about the 22.5's... they generally last as long on the coach, if not longer, than they last on the rack.. The major damage is sunlight, not millage.
Home is where I park it!