For stores with low populations, has the store been promoting heavily within the store and on various gamer sites? I've never had a problem finding gamers. It can take time to find them, but if there is a gaming store someone is buying stuff and would be interested in trying out D&D.
The store I am running encounters for will post any advertising that I give them. I also made up a 'RPGA Business Card' that the store has been great at giving to anyone that purchases any D&D materials. It pretty much just contains my contact information but they are also promoting Encounters to anyone that gets one. (They are excellent to work with in this aspect!)
Based on the last couple of weeks, and University starting again, I am expecting an extra table for Season 3 (currently run 2 tables).
I'll be using the 3rd table as a 'test run' for any of the players that have been playing encounters and that want to give DMing a try.
I find that word is spreading, and more and more people are showing an interest... it just seemed people are reluctant to get into something like this over the summer.