Go to either (or both) savta.org and clearstar.com. Both of these sites are for professionals in the security business, and have a feature that allows you to search for those that have businesses in your area by zip code.
If there was a particular manufacturer you were looking for, most have dealer locators on their websites as well.
If you happen to find somebody that's on your manufacturers's website as well as the savta or clearstar website, I would start there.