To do a better, wider search on craigslist, use this website:
http://www.searchtempest.com/
It will also give you eBay listings and search several cities at once.
Another source is:
http://vehicles.oodle.com/trailmanor/
However, Oodle has a habit of not clearing old listings.
Be prepared to travel a long distance to get the trailer that you are after. Determine the max that you are willing to travel when designing your search. Just be careful about that because id you put 250 mi and there is one 255 mi away, you won't see it. IMO, It's realistic to expect to travel 1000 mi (each way) to find the right TM at the right price. It they are priced right, they sell in a day or 2.
A couple of times, I have driven 100 miles to see a trailer at a dealer only to find that someone bought it while I was en-route. I've never had that experience with private parties. We drove 1100 miles (each way) to pick up our 1st TM. The seller told me that he had several (phone) offers for thousands more while I was en-route. I believe him because I had the same experience when I sold that trailer a few weeks ago. He held the trailer and sold it to me at the price listed.
I bought my current trailer from an ad that was posted on this website. The trailer was ~100 miles away. I was at the sellers house within 3 hours of the post on here. The short and long of it is, be prepared to purchase if everything is right. Be ready to go as soon as the ad is posted. If the price is right, most TMs sell in a day or two but often
within a day of posting if the price is fair. Plan on spending $1000 - $1500 after the purchase and you won't be disappointed. If ypu think that you are going to by any trailer, drive it home and not have to correct, update or repair things, you're setting yourself up for a disappointment.