Hoye tractor can get you rims most likely. As for tires......almost any local tire store can get your tires.....they're expensive to ship so I would look local. I purchased front tires for my tractor from a local Tire Factory store. If you search "tractor tire and rims" on the Web......you'll get lots of hits. You won't have problems finding what you need. Hoye is great for any other parts you might need.
I don't know if it helps any, but my YM240 has Kubota rims on the original Yanmar discs. (See my Sig, below). Presumably new tractor take-offs. That might broaden your local search, to ask at your Kubota dealer.