I believe C. B. Tatone makes a cast "Pitts" type that would fit. It straps on with a strap clamp. Just go to your LHS or Tower Hobbies and search under "muffler". May take a while, but you should come up w/ several choices. Good luck.
GK1, Have you checked out Mac's Mufflers yet? They carry a lot of pipes for a lot of engines! Even some one piece mufflers that are a good replacment and are a lot lighter too. I think Tower sells them.
Suptter