I am in the Tampa bay area and got most of my mango trees from Squam (Alex - Tropical Fruit Acres in West Palm Beach) and Truly Tropical in Delray Beach. I first bought trees from Alex when I stopped by his place a couple of summers ago to buy fruit and I got another tree from him a couple of weeks ago. This time, I placed an order online and he had it ready for pick up the next day. Great customer service and I have always been more than satisfied with the trees I got from him.
Har helped me pick the trees I got from Truly Tropical (I bought six from there about a year and a half ago). Very happy with the trees I got there, too.
I have bought a couple of mango trees from Excalibur. While, they did not look nearly as good (they were pretty rootbound) as the ones from Alex and Chris/Har, after a hard pruning, they have recovered and seem to be doing well.
Another place to try is Lara Farms.