Mounts botanical garden is a very decent place and they have a ton of mangos and other tropical fruit trees. It’s a bit of a drive from Miami though.
https://www.mounts.org/
Being a bit of a drive from Miami is often a positive.
Lol...Murahilin, I agree 
Miami (and parts south) is awesome, just gotta know where and when to go. Would much rather be here than...
Serendib and Lara Farms may have some fresh fruit, and Robert is Here is worth checking out. Fruit and Spice Park, Fairchild Garden, Fairchild Farm, and Kampong are all worth a visit. Frost Museum is a lot of fun, I especially like the top levels where marine life and terrestrial displays meet. No fruit tho
Loquats, carambola, and sapodillas are ripening now, Indian jujubes just finished up. Got some noni too, lmao