Re: Exhaust can/box muffler?
Look for the muffler from a Husquvarna 372 chain saw. That saw was 71cc's but they used the same muffler on the 365 which was 65cc - so the volume should be right for a china girl engine.
Price is less than 20 USD on e-bay. Should be able to get one in OZ for a reasonable price.
You will need to make an adaptor plate to mount it to the china girl. Not hard to do.