There's a few places:
1.) Go to TicketRES on this board.
2.) Buy them at Sea World's website,
www.seaworld.com.
3.) Buy them at a 3rd party ticket place. I've had lots of luck with
www.ticketmania.com. There are many others that sell tickets.
4.) Sometimes
www.ibidUSA.com will have Sea World tickets for bid.
5.) Buy them at the gate.