The campsites by the coast go fast in summer. Forget 8am, if you are not ready by 1am, to the day 6 months before you go camping, all good sites are gone.
You have two options:
1. Many of these sites set aside some campsites for those that drive up there on a first come first serve basis. These are not part of the reservation pool. You can take your chances and try that. But it helps to have a backup plan if the campsite is not available.
2. Try only those campgrounds that do not take reservation or try the private campgrounds, these will be expensive but not as sought after.