I have a leak in my power steering.

Do I need to buy new or can it be rebuilt?

The gear or the pump? I know for fact that the gear can be rebuilt, I did it, probably going to swap to the hi performance one anyway though. Not sure about the pump, never looked into it.
Got the gear rebuild from O'Reilly's, any auto parts store should have it, might have to be ordered though.

Yes, you can buy the rebuild parts for the power steering pump\reservior and the power steering box, from the auto parts store. If it's the pump\reservior, they're $75 for a whole new Cardone unit. You can get the steering box rebuild kit with the seals, etc. very inexpensively as well.