A lot of TRUCK STOPS usually will sell some scanners. But other than Rat Shack as far as retail goes you're going to be limited. If you deal in cashless (ie. you have a debit card or credit card) its actually better for you to just go ahead and order online.. You have several choices.
SCANNER MASTER.com which is an official supporter of this site is a very huge resource for all of the popular brands. If you do a google search for buy police scanners you'll come across several sites you can order from. Do you know what it is you're looking for in features? Do you need a mobile or portable, digital or not, trunk-tracking or not?