It seems that my Low Tone Horn has gone DEAD!!

Does anyone have an idea as where I can purchase a used but working Low Tone Horn? How easy is it to replace and if it is not too hard, does anyone have instructions as to how to replace the horn?

 

www.shokan.com for all audi used parts. You have to remove the bumper most times to get out both horns, sometimes you can get them out by pulling out the lower grilles.