I was thinking... on my Softail, I deleted the cowbell and put two Hella Compact Trumpet horns behind the transmission, in front of the back tire, where the vapor canister should be. The Hella horns are about the same diameter as the vapor canistor, so with some creative mounting, they fit very nicely in that space. I suspect that the same might work on the touring bikes (horn where canister goes)
I think I paid about $20 for the set (high and low note) online. These horns will wake the dead and are virtually invisible on my bike... sounds like a Caddy when I whack the horn button. Scared the crap outta me the firt time I tested them out in the garage!
http://www.hella.com/produktion/Hel...ies/Horns/Compact_Trumpet/Compact_Trumpet.jsp
They can be found in black as well as the red if you look around.
Also, your stock H-D horn is a Hella Compact Trumpet horn, low note, I think (it's stamped on horn body). Same horns are used on Hummers, last I noticed.
Make sure you use a relay (fused) if you add a second horn!