I found someone locally through 3Dhubs.com. I brought over a melodica and mouthpiece and he made drawings based on the mouthpiece and tested the fit on the melodica. I wouldn’t characterize these as flexible; the Hohner mouthpiece design is pretty thick, compared to say, a water bottle, and at that thickness they just feel solid.
I rinse them well but I haven’t been sanding them. I suppose if you played for a very long time at a stretch the layers might irritate your lips. That hasn’t been a problem for me. PETG is sandable so it would not be difficult for someone to shape and smooth it to their taste. Do you mean a finish like some kind of clear coat? I don’t know what would be a safe coating. I think it’s better to leave it as-is. But I’m open to suggestions. My thought is to keep it simple and the price low and if people want to modify them they’re welcome to. I don’t plan on turning this into a business… when these are gone, that’s it.