Jim, in my case, the Deere guy is a couple or few miles north of me in Union, MI. I'm sure that he isn't the cheapest, but he did set me up with a couple of new rear wheels and tires for my 4520 a few years ago. I don't recall what I paid him, but recall that it wasn't out of line or take me. These days, dealers are hungry like the rest of us and will deal. At least my guy does. For my Massey or little Allis, I can still go through him for parts, and do on some, but mostly a bone yard about 10 miles south of me if it involves metal. They usually can set me up, and I could buy entire tractors from them. Had I been interested or needed a Ford 9600 or 8600 a couple of years ago, or a wide variety of others, Myers in Wakarusa, IN could have set me up, even delivered.
I guess my point is, your nearest tractor dealer or bone yard on the wheels, and tractor or AG tire dealer on the tires.
Good luck Sir.