Not familiar with that model, but if it runs the 6-12 size tire like mine does, those wheels were used on very early Cub Cadets and Wheel Horse tractors. And probably other make garden tractors too.
If I was looking, I would try Ebay and also any local tractor shows in your area. Most times (here in NC at least), somebody is selling lawn mower parts at the tractor shows.
Your local Craig's list and Facebook Marketplace may be another source.