By the way, those are both nice trees on the Growing Ground site...Prices aren't bad either.
If I were looking for sizeable deciduous specimen trees in Fla., I would not go North to find them
. I would go west along the Gulf--to La. and Texas. You're staying more in the "compatibility zone" if you do that and will probably have more luck with trees that will be relatively problem free in Fla.
For instance, Guy Guidry at
http://www.bonsainorthshore.com/bon..._site_index.htm
probably has some interesting stuff. In particular, I'd see if he had bigger native hackberry, cedar elm, or other S.E. native specimen deciduous species on hand. It might be worth a telephone call to see exactly what he has, as the web site changes very little. He sells on Ebay and has listed some very nice native species there from time to time that have not been on the web site. I've also seen him in person at the Bonsai Convention in D.C. a couple of years back. Very nice trees...not cheap though, but not "hack and run" jobs either.
There are also a few sellers in Texas with some nice stuff...