like Jim said too, the x series up to 25 fit this little gem too.
i think i found one that is the 1 piece design, but i'll have to buy the whole engine package to get it...............

2nd choice would be the K&B style and thx for posting that info.

w8ye-thx for the mac tip...........only thing that bothers me about their muffler is i know 2 people who used them and complained of overheating..........of course the NV could have been set wrong, but they did lose power with them as well.