Here's is the best place to start:
A Post-It-Yourself site:
http://www.sailboatlistings.com/sailboats/CSYThe Yachtworld Site, searching on CSY's from 33' to 44', $15K-$200K:
Click HereNote: When you go to the YachtWorld site, if you want to be notified if new listings are posted, scroll down a bit and on the left side of the page, there is a 'Notify me when more boats like these are available ...'.