You might want to give these guys a call. Here's their website >
http://www.carhornrestoration.com/index.html
The Horn Works
Restoration Specialist of Collector Car Horns
967 Hackett St. Beloit, WI. 53511
608-361-0095
Mon- Fri 9 - 4 Sat 9 - 1 CST
Est 2002
The site says 1956 or newer car horns but maybe the can help you out anyway or refer you to someone else....