The only ones I have found that work are the originals (that break easily), a Rovner fabric type and the original Harrisons. I have a NOS gold plated Harrison that was made for the Selmer altos but it is really expensive. Never really used it as I sold the mouthpiece while I was a Harrison dealer in the 1970s. Probably a Rovner would be your best route. I haven't found any clarinet ones that work due to the shape of the sides of the mouthpiece.