Other than the Casita and Fiberglas RV forums and facebook pages, a couple of search tools may help your search.
One is searchtempest This site allows you to search all craigslist sites with one search. Enter your search criteria and the distance you want to search and this tool does all the work (except ruling out all the scam ads for casita and scamp...)
The other is rvtrader. Set up an account, do a search (for casita or whatever) and save it. When new ads are posted you will get an email. This is how I found our recently acquired Casita. The ones you find here will most likely be from dealers that typically know nothing about Casita trailers.
I wouldn't think you would have much trouble in Florida. I've seen quite a few there over the months I've been looking.
One other bit of advice I've learned from these experienced folks is beware of 'soft' floors. The only structural wood is in the floor and water leaks or flooding in the trailers history can rot the floor which is a major job for replacement.
As for your tow vehicle, I'm using a Ford Ranger with the 4.0L to tow my 17'. It tows fine, but I definitely know it's back there when towing uphill.