Small Engine Troubleshooting Problems? Ask a Mechanic Now.
You will be hard pressed to find a new flywheel. Is this a horse model tiller. If so then I would recommend that you do an engine repower with a briggs 6.5hp. I have done several of these swaps and they work great.
http://www.smallenginewarehouse.com/RepowerItems.asp?Brand=Troy-Bilt&Model=Horse Tiller / OLDER 2 SPEED