They are all over eBay from various dealers. Check out the auctions and see if any are in your neck of the woods. Here's some links from when I was considering this route. I have since decided to mount a channel in the bed of my pickup and forget the trailer.

http://www.suncoasttrailers.com/main.html
http://www.1-stop-guide.com/trailers/trailers.html
http://x.scandipacific.com/index.php
http://www.readyramp.com/index.php
http://www.trucknamerica.com/serv01.htm
http://www.kendontrailers.com/
http://www.sportutilitytrailers.com/LongChih/749TC.htm
http://www.campoutinc.com/

"Never underestimate the power of human stupidity" - Robert Heinlein