Really tough to get beach spots now in the summer weather. I have a spot at San Onofre on the bluffs for next month. Emma Woods and the other beaches next to it are almost impossible. Reports on line indicate that there might be problems in that the local fire dept and police dept are holding spots. I can't verify this.
Several of the CA state beaches are reserved through reserveamerica.com but not all of them. Check also with the different cities and counties.
After Labor Day it may be easier to get, as that day marks the unofficial end to summer season, and kids go back to school about then.