If you have no lick on this site, keep an eye on ebay for terms like "vintage ford horn" or "flathead ford horn". A quick check just now only came up with a couple close ones, but they do show up there.
https://www.ebay.com/itm/Vintage-6-V...QAAOSwVQhgOEny
https://www.ebay.com/itm/Vintage-Mus...kAAOSwUjpajxlF