You will need to contact Trefussis estate agent then you will be able to be allocated a space on the beach. (Cannot remember the phone No)
parking the car can be a pain especially during the holidays, get there early to get a space. Sure somebody will be along soon with all the info, Fal HM may have contact details.
If you get stuck going down the official route have a beer or two in one of the pubs in Flushing - somebody will know someone who can help. That's how I secured a spot for a 16ft run around right outside the Seven Stars although it was a long time ago