It's going to be tough to find one last minute. In my experience, they usually sell those out pretty fast. I believe you can always go to the cabana area on the day of and check to see if there are any no-shows. Sometimes you can get on a wait list the day of. But you'd need to get to the park early so you're one of the first ones in the gate, and head straight there first thing to see if you can get on a standby list. Good luck!