This is one of those situations where I had about 5 of these several years ago, and sold them off cheap at a show because I (get ready to quote me here....) "I'll NEVER need one of THOSE......."
Here's a picture that I found online of what I'm after. Either the stamped round metal horn, or the stamped petal type horn (think Paillard, German machines, and the like. )
Thank you for looking (and helping in the search!)