Below is a link to Op Ed and LTE guidelines for the top hundred papers, by circulation, with links there to their online submissions. It's something I have bookmarked. You could hit 'em all if you want, and the odds are on your side if you do, although, since the guidelines vary, you won't really be able to send the same letter to all of them unless it's really short (not that that's a bad goal for LTEs and Op Eds anyway. ) Anyway, thought some here might find it useful. I know I've posted this before, but I can't find it anywhere, and, since I know what I'm looking for, I doubt many others can find the old one either.
http://www.ccmc.org/oped.htm