Hmmm... tough one. First you need a big hat and a personal fan for Miami
in July! The only thing I can think of is finding docks where liveaboard
cruisers might be and just walking the docks and having conversations. Fort Lauderdale
might be better for that but I'm not a FL resident so not sure. (spent a bunch of time there though) A lot of liveaboard
cruisers are hidden away from the mainstream... and in July they may be elsewhere! You could find some boats avail in the area and arrange to look at them, in the process you would find possible places where you can do what I suggested above....