How can I access information about casting calls being held?
Facebook has local acting resource groups in most cities. They are usually independently moderated. There are also auditions on Craigslist under "Talent" and "Gigs". Most pro auditions should be held in commercial spaces. Always be careful when answering a casting call and try to bring another person if possible. It can't hurt to contact talent agencies to find out what they require to represent you. It can range everywhere from an extensive film demo reel to a simple monologue performed in their office. Good luck. I think acting is the best "job" in the world and I wish you a ton of success.
I would recommend Backstage (www.backstage.com) or Actors Access (www.actorsaccess.com). I used both when I was living in New York and my agent here in Houston uses Actors Access. Both of them have notices for Florida.
You don't need an agent for either one. Both have subscription options to submit online, but I would poke around before committing.
Another suggestion, casting agents will occasionally post workshops on these sights and SOMETIMES they cast from these workshops. I say SOMETIMES because it's easy to get your hopes up, so don't be the farm on it. There is usually a fee for these workshops. However, the closer it gets to hundreds of dollars, be cautious. Do your homework. You will be able to tell a legit agent from a simple Google search. And when in doubt, throw it out.