Hit up a phone book and look in the yellow pages...under Stereo A/V dealers or something of the sort (Stereo A/V dealers is what it's listed as in our phonebooks)
Go to the magazine rack at almost any store that has either Mobile Entertainment, or Car Audio magazines....there is almost always a list of reputable shops in the back few pages of the magazines. I've found quite a few shops that way.
There's also http://www.yellowpages.com //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif