There was a post about paddleboard rentals a little while ago, here your answers:
Stand up paddle boards for rent directly on the beach located at the Negril Relax Resort which was the old Merrill's III. Feel free to call for any information. Here is his Jamaican cell # 876-588-4574. $20 per 1/2 hr and $40 per hr. I don't know how early you can rent but I'm sure you can work something out. The person who rents them is on the board, I would PM him. Mnball is his username. I will be calling him in March...
Here's the thread:
http://negril.com/forum/showthread.p...t=Paddle+board