In addition to Steve at Coconet, you might try Castle Cars and Moncho's. I've previously rented from Monchos (they're right next to the airstrip) and received good service with an electric cart, but I've never rented gas cart.
Steve - I'm not familiar with how you operate - do you own and rent carts, or do you outsource to other companies?
Personally, if gas carts are as noisy as some have described them, I hate to think of them in San Pedro....