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....