I was faced with similar problem;
19" mitsubishi rims.
Searches led to like well over $500 for a USED! (+shipping)
I went to a big truck tire shop * that told me that they had a welder that would weld/patch as required to 'get her going' for a flat $50.
They would then have added a liner to cover the welds and protect the inner tube.
Note that balance on a tractor is not necessary due to low speeds.
Luck had it that my rims were fair and when mounted on the big machine, they, with a grinder powered wire brush polished the rim and primed it for protection.
New tires and inner tubes + juice for weight cost me $900.
Calcium cloride is what was eating my rims.
Only solution tractor places had was 'new rim', no alternatives.
Last 2 tires my size in Canada!
Should be good for another 18 years.
My treads were still great but the weather checks were down to the cords and I feared a blowout at any time. Most probably at -30 and 5 miles by foot from home, LOL.
I call it insurance!
*BIG, like a semi was there installing 18 big tires for something like $5000.!