Good luck on that one! Try searching for salvage tractor dealers. One that will put your request out on the parts wire. Thats a request line they are subscribed to.
When mine need a tranny thats how i found one. Then my dealer talked me into rebuilding what I had. Good reasons both ways. The one I found online (can't remember where) was about 1000.00.
Whats wrong with yours?
Rory