Griots Garage offers a pair of Hella horns of 118 db.
GERMAN HELLA HORNS. LOUD AS CAN BE! $69.95
Tired of those wimpy, factory installed horns? You'll get some respect with these. I only honk my horn when it's absolutely necessary. For those times I do honk my horn, I want to be noticed. And just in case you haven't noticed, stereo systems are getting louder and interiors are getting quieter, which means you need to be heard! Plastic? No way! Durable, metal casing for years of survival. Easy installation. If you have horns presently, just swap the horns and use the existing wiring. If you want to add them to your present horns, a relay and directions are included. Loud as can be! 118 dB. Stoutly made in Germany.
http://www.griotsgarage.com/catalog.jsp?&SKU=77573
Roscoe