Easy.  Go down to Bill Baggs Cape Florida State Park on Key Biscayne when the weather gets cold.  They rain from the trees, and lay dormant on the ground until the sun comes out and warms them up.

According to the Miami Herald, the locals aren’t too fond of the iguanas, complaining they munch the local hedges and gardens.  One commenter says, "If they are a pest why not cull them while they are laying around comatose?"

Dude, they’re lizards, not rats.  I’d fill a sack with them, take ‘em home, and start my own iguana ranch.