ImpalaSSforum: http://impalassforum.com/noncgi/ultimatebb.php?ubb=forum;f=12
NAISSO: http://www.impalasuperstore.com/naisso/classifieds/viewads.asp?catID=4
eBay: http://motors.listings.ebay.com/_W0QQsocmdZListingItemList?sofocus=pf&sbrftog=1&fcl=3&socmd=ListingItemList&catref=C3&frpp=50&from=R2&fccl=1&satitle=&sacat=5346%26catref%3DC6&a39=1937&a41=10375&a38v1y=1991&a38v2y=1996&a10239=-24&a39705=-24&a10244=-24&alist=a39%2Ca41%2Ca38v1y%2Ca38v2y%2Ca10239%2Ca3801%2Ca85%2Ca10246%2Ca33512%2Ca10241%2Ca10244%2Ca39705&pfmode=1&reqtype=2&gcs=13&pfid=2473&pf_query=&sargn=-1%26saslc%3D2&sadis=200&fpos=77016&sabfmts=1&saobfmts=insif&ftrt=1&ftrv=1&saprclo=&saprchi=&sadis1=100&fpos1=77016&lsot1=&fsop=2%26fsoo%3D2&coaction=compare&copagenum=1&coentrypage=search&fgtp=&sadis2=100&fpos2=77016&lsot2=
Craigslist: http://www.craigslist.org/
Autotrader: http://www.autotrader.com/
I would definitely look at the first two website first, since those guys really care about their cars and know more about them. For the lost part, they are straight up with you about their cars.