That would require defining 'mainstream', 'cause our local Alternative station plays them. Which, I might add, has been one of the most prominent stations in the Tampa Bay area since it started broadcasting in 2000. The styles have shifted over the years, of course: 10 Years had their heyday ~2005/2006, Rise Against has been constant for nearly the entire time, Cage the Elephant is current enough.
I stopped listening to most of the current stations 6 or 7 years ago, since I got sick of all of heavy rotation and small number of artists/songs that get played (and I haven't been too enthused about the genres that have taken up mass popularity; 90s Post-Grunge is the only stuff within that genre that's actually worth listening to*, and I can't stand the indie folk hipster crap everybody was swooning over a few years ago...the pseudo-lo-fi stuff getting passed around now isn't much better).
*somewhat fittingly, 90s Post-Grunge (or heck, Grunge proper) is rarely played on the radio outside a few artists, and only a slight handful of their songs at that.
My general route of finding music is more through watching AMVs or through forum talk, hearing something in the background of a television program/movie, browsing iTunes' and Amazon's free offerings, or finding the occasional streaming radio station to listen to. The radio or MTV/VH1 play into it very little (because on a rare occasion they still do, like once every four or five months, if that).
