They were pretty common on the P series forward control trucks, plus there's several companies that are making them new, in both single and dual wheel version. As far as tires go, I would suggest getting new, rather than trusting a used tire, unless you 100% know the vehicle it came from. Too much risk of a zipper rupture if the tire has any damage, especially from a runflat situation.
This company manufactures 19.5 wheels. Might be worth checking out if you don't find any used wheels.
