I happen to see these in my local Publix in the Tampa Bay area. At $4.99/lb they are a little pricey but worth a try. I've never had one before but after reading a little about them I'll certainly give it a try. Sounds delicious.
I'm not sure if the trees down there are fruiting right now, but if you see one in someone's yard, just knock on their door and ask. Robert is Here is another good bet.
They are hard to find but you could try Waterfront Market. If you do not see them out front, ask one of the clerks to check in back. Flamingo Ice Cream also has sapodilla ice cream sometimes.