The Piano 36 is an early 1970s instrument, maybe introduced in 1969. The trumpet mouthpiece for the Piano 36 is the HMA-81 (which I believe is the same as for the Professional). The mouthpiece hole of the Piano 36 is smaller than most. It is about the same diameter as either end of the typical melodica hose (tube). Melodica tubes (of any brand) have two fittings, one a mouthpice and the other that (of course) has two ends, one fitting into the instrument and the other into its end of the tube probably will. If you remove the instrument end fitting from the tube, its small end may fit into the mouthpiece hole of the Piano 36. I have two of those fittings in front of me. One of them fits perfectly, the other is a bit too small. I don’t remember where I got the one that fits perfectly, but I’ve been using it for some time with my Piano 36, and it works very well if you like a short (1.5″) round mouthpiece with a small circular opening. If that fitting fits, though, the mouthpiece fitting at the other end of the tube probably will. Here’s the kind of tube with fittings that I’m talking about, although the fitting on this one does NOT fit the Piano 36. But if you have other melodicas with tubes, you could try their fittings. Below is the HMA-81 trumpet mouthpiece. I hope this isn’t too confusing.