Finding good mud in Florida is not as easy as it seems. Some mud in Florida is tidal, and best access to such places will be by boat. Other muddy areas are dependent on season. We are currently in the winter dry season. It still rains but the ground has been dry for a few months, so rain gets absorbed into the dirt. So there is less chance to find mud.
Curiouspaints is partly correct, there is a danger of Alligators in Florida and because of that, I would not recommend you play around lakes and ponds, ..but during this time of season, you will not see any because they don't like cold and are in hibernation.
Speaking of cold, sadly your timing is bad. Next week, the weather is predicted to be in the mid 30s to 40s F. (Depending on which part of Florida you are visiting) as a cold front is expected to be moving thru the state by the weekend.