You can purchase good ones at MegaMart on the way in to Negril from the airport. You can get booze, drinks and ice at MegaMart - so you can have full artillery at your disposal before you leave the parking lot... and there is an ATM machine inside the store to make it just that much easier... oh....
And they also exchange US$ at a decent rate....
This is what you could call a "no-brainer"... (grin)