Welcome aboard, kayakgal.
We got our used 19 by a combination of diligence and luck. Had been looking for a couple of months with no luck when the trailer we purchased showed up while I was literally logged on to this forum. Had been looking for a 17b, but this one was priced right for what it was by the seller, and after calling the seller, we were on her doorstep the following weekend, 300 miles from home.
What's said above is very true--if you want to buy used, you have to look hard, be lucky and be flexible about what you will accept. Winter time does seem to be when the most trailers are on the market. We also had an honest seller--when we got there, she had several others who really wanted that trailer and she probably could have played us off against the others if she had wanted to. Even knowing there would likely be issues due to the age of the trailer, we made our deal on the spot.
As was mentioned above, many hopefuls see the prices of the few units that come on the market and ultimately decide to buy new if their budgets allow. Not an option for everyone, though.
One other thing: Karma dictates that the "perfect" trailer will show up a week after you finally settle on an "acceptable" one! Don't look back, life isn't lived in the rear view mirror.