Since we have a number of threads that also delve into where to buy etc. I going to suggest using this stickyhttp://www.avsforum.com/avs-vb/showthread.php?t=937822
Or use common search words like buy,ebay or used in the advance search engine, title search only for related past threads. But, the bottomline is go where you'd go for any used electronics...
classifieds here, Home theater forum etc