Here's my old idea, after you find the neat utils to check craigslist.. I use craizedlist.org, it lets you set and save your searches, and pick which cities you want to searc. NOTE, like the site will tell you, no way around it, you have to use FIREFOX, NOT Internet Exploder, to use that site..
To find bikes forsale, one dang good resource was the "United States Trials Club Directory" that used to be on the NATC (now called mototrials) site. They removed the list and it was put on another site. I havent been to that list myself since 2010.
I believe I put the link in this thread, back when, but due to time I dont have time to hunt for the link right now, for you all, someone please look through? http://www.advrider.com/forums/showthread.php?t=486887
Most clubs have forsale pages, not all. Here is the link to clublist! http://www.trialsclubs.us/
Everyone should help out on this, if you have website and know it is not in here, or has changed, do what the page says, email someone.