Might want to check out Hadley products.
www.hadley-products.com
They list all kinds of compressors and air horns. I picked up the Hadley Bully-Electric Dual Air Horn Kit (code: XXXH00961EA). It's real loud! Dealer installed compressor and horns between grill and radiator. Hooked the horn wires right into steering wheel horn pad. Threw the wimpy factory horn away. Horns are metal so they won't crack in freezing temps. Plus, it comes with an air hose that attaches real easily to compressor through the grill slots. The one I chose is a bit pricey, but I figured with air horn and air hose - it's kinda like a "two-fer".