Keep looking for that muffler, it may take 1 day or 1 year or anywhere in between. Do a *bay search for OS30,35,40 engines as sellers sometimes have the muffler with the engine they are selling. Besides, as a bonus you'll get another engine. And we all know that you can never have enough engines
Fuel - sorry - must be ALL CASTOR - please re-read my earlier posts & also the post of Downunder - use anything else & your engine will be worn out in record time.
You can mix your own brew of all castor fuel - check out the RC Universe fuel forum for details