I've got no experience with engines that small, but I do know that the larger Magnums use the same mufflers as the equivalent OS or ASP engine. You might try [link=http://www.bissonmufflers.com/en/muffler.html?mufflers::listing_id=1135793]this bisson muffler[/link], but I'd be inclined to email the owner of Bisson first to check it'll fit. He's a nice guy, and very helpful... even going so far as to put pics up of a muffler I was interested in but wasn't yet pictured. Even if that muffler won't fit, he will also do custom mufflers.

Matt