I've seen guys getting on the bus to Wong Shek with surf boards before.
You could always get a speedboat from Sai Kung public pier - cost may 400 to 500 bucks though.
The only other thing I can recommend is to contact the owner at Hoi Fung store in Ham Tin Wan (Tel: 2328 2315). It's a noodle place that does board rental as well - just not sure how long they are. No harm in phoning them up and asking. They also organise kaido trips there - but the catch is you need at least 8 people (cost is $100 per head, minimum charge of $800), so you will need to find some other buddies headed out that way to share the cost.