It is hard to know what you will find but EBAY is a decent placce to watch... I bought my Atlas Lathe, Bridgeport Milling Machine, and a Pantograph Mill (well a Giant New Hermes Engraver) all off ebay....
I have this page (I am going to be reprograming it soon) that I still use to keep an eye for parts or accessories that I may need or want...
http://www.lathetalk.com/ebay/index.php
The trick is deciding what you want or need and then be patient enough to pick up a tool at a decent price...
You might also look for places areound you that sells used tools... Obviously shipping on big tools gets very expensive and I drove about 11-hrs round trip to pick up my Bridgeport so a local place would be ideal.
Good Luck and like I said I will be updating that page soon!