I frequently go to my local craigslist to see what kart related stuff folks have, but there is not usually much racing stuff there, and this is in an area that has a track in it (East Lansing Kart Track) and several more tracks if you don't mind driving. On a whim I searched the Indianapolis craigslist and Jackpot!!! Check it out:
http://indianapolis.craigslist.org/search/sss?query=kart&zoomToPosting=&minAsk=&maxAsk=&sort=rel
http://indianapolis.craigslist.org/search/sss?query=kart&zoomToPosting=&minAsk=&maxAsk=&sort=rel