I'd just recommend using Pandora or Spotify online, they're not perfect but I've found a couple new bands through it by putting in Gaslight. The radio stations that play Gaslight are standard alternative rock(104.5 in Philly for example) and pretty much stick to billboard charts so you probably won't find anything new.
Here's a decent list of bands you should check out:
http://www.last.fm/music/The+Gaslight+Anthem/+similar