Holding a Zink is a challenge. It takes time to get comfortable. They make those small acorn mouthpieces just to keep the embouchure development equally slow. In all the research that I have done, I have discovered old instruments but no original mouthpieces. I am pretty sure that most cornetto makers had, like modern trumpet companies, their own mouthpiece recipes. I use a Moeck acorn mouthpiece made of brass. It is about 7C diameter but has a deep acorn cup.