Brian,

I have about 4 horns that do not work (and three that work) and I have been waiting to see if anyone had any recommendations.

Here is what I found a while ago from a websearch. I know nothing about these companies:

Repairs: http://vernco.com/id516.htm

Restoration services:
http://www.classiccarhorns.com/proc1.html
http://www.carantennas.net/car_horn_repairs.htm

Tim