Red banjo horns alternative source?

[HughH]

While the majority of the parts for our cars are specifically made for them, either by Porsche or outside suppliers, a substantial number were also off the shelf items from suppliers, or common with VW, 356's and some other German cars etc.

I stumbled across these listings for the banjo red horns made by Bosch, for cars up until late 1972, that lots of people seem to be looking for.
here is the ebay link

These seem to be for a motorcycle and appear to be identical to the "tief" of high (small) horn I have, except for the washer on the mounting bolt on mine which is stamped "tief" with the numbers 0321023019 and 12V. That washer appears to be missing on the ebay items (there were 3 of them all using the same photo when i looked) but the numbers stamped on the actual horn looked identical.

PS I have no affiliation with these (although i did think about buying them to corner the market )

Maybe we need to start another thread somewhere where alternate sources / uses of some of the hard to find parts can be cataloged?