They're everywhere on eBay?
http://cgi.ebay.com/MARINE-AUDIO-EQ-...item4cf8665dd2
It was fairly easy to install, just takes quite a bit of RCA cable if you mount it under the driver's console like I did. I mounted it there for two main reasons.
1) I bought the thing so that I would have easy control of the volume. I like to be able to turn down the volume when I'm trying to concentrate, someone turns it up too much, or I need to say something.
2) I LOVE the PA mic feature, having it mounted under the driver's console allows me to use the mic whenever I want to talk to my rider/skier.