Muffler making is somewhat of a cottage industry. Some of the top makers included Tatone, Macs and Slimline. Others got into it as well, including Big Art mufflers in the stunt world. While the welding and finish on the Macs is surely impressive, the tolerances required for muffler making are not as exacting as, say, P/L fit. The rights and tooling for Slimline are mow owned by Desert Engines, but they only bought the business to make their own mufflers, not the complete line.
I'd like to buy a Slimline tongue muffler for a Veco .19 our club uses on a trainer, but they are quite rare. So, probably I will either need to get access to a mill or get a machinist order together.
But, if you want a copy of the Macs for the K&B .40 or a complete K&B .40 R/C, that I have for sale, in quantity.