i would check for 12 Volts at the terminals that plug/connect to the horn to verify it's the horn, not the wiring to the horn. then i would go to FLAPS (advance, auto zone, olympic...) and get a cheap VW replacement horn (or go to junkyard...) but for the price, new would probably be more cost/time effective. then i would put "a real P-car horn" on my shopping list for Hershey....
if you get in a bind, i have said VW horn... somewhat local (vienna)
why didn't you register your car as an antique? no safety inspection required in exchange for somewhat limited use..... unless yours is a daily driver....