Most will have more organics in thier soil for tropicals, I add a bit more in the pine bark area to the basic bonsai soil mix. If you need to ask what that is I would suggest contacting bonsai nurseries closest to you and talk to them about what works well for your area, you are hotter that I am up here in Massachusetts.
I have seen in a couple of places where the mix was less organic, and typical free draining soil, the idea was that the roots would get more finer feeder roots if the soil was kept drier. Any clubs in your area? Info from a local club should be the best info you can get. Worst case get a hold of Dallas Bonsai and pick thier brains.
Going back to soil, I would skip the Walmart stuff, and do a search for soil mix/soil recipies on the bonsai forums, and read read read, bottom line is you have to find out what works well for your specif location.
Where to get it you ask, well you were going to ask weren't you, check bonsai retailers, Dallas Bonsai as mentioned before, Shady Side Bonsai, Bonsai Ideals, all sell a quality soil mix. Check also the link section right here on the Bnut.
A good source would also be to give Irene B a pm and see what she suggests, she is also down in the oven you guys call home.