Yeah, the waiting game is hardest one! Any marina or marine store should have the appropriate locks. I would suggest getting a matching (keyed alike) pair for the both the draw bar and the coupler. The coupler lock will be long, thin rod that goes through that hole in the coupler. It's a very common item so it won't be hard to find. It looks a lot like the securing pin that holds your draw bar in. The reason to also have a locking draw bar pin is so someone, while you're out on the water or parked at a restaurant (back on the trailer), can't slide the draw bar out of your truck... Push the boat backwards... And slide your draw bar (still attached to your coupler since it's at least locked there) into their hitch on their truck.