You might try Assateague Island, just south of OCMD. If you don't mind walking a bit from the parking lot area, you can most likely find your own slice of the pie. The downside is that there's a vehicle entrance fee to the park, on the order of 15 bucks.
If you go to OCMD instead, surfing is only allowed at two blocks on the public beaches. These blocks rotate daily. On Labor Day, those two blocks are 41st and 121st streets.
If you already have a "National Park and Federal Recreation Lands" Annual pass ($80 for 13 months), you should be able to use that to get in at Assateague. That pass is good for any National Park, and includes great surfing spots like Hatteras, Cape Cod, and Assateague National Seashore. You can probably inquire at the gate (or visitor center), if such pass would be beneficial to surfing and other outdoor recreational activities.
What’s the difference between the National Park and State Park day-use areas?
The State Park day-use area offers a concession stand, warm showers, flush toilets, camp store, and life-guarded beaches (10 a.m. to 5 p.m., Memorial Day to Labor Day). The State Park day-use service charge is also good for use of the marina for clamming, crabbing, and fishing. (Use of the boat ramp is covered by a service charge of $10.00 for Maryland residents and $12.00 for out-of-state residents.) State Park day-use charges are $4.00 per person for Maryland residents and $6.00 per person for out-of-state visitors (cash or check only accepted at entrance station). During the off season, the charge is $3.00 per vehicle for Maryland residents and $5.00 for out-of-state residents. Golden Age Passholders and children in car seats enter free of charge at all times. Annual Passes may be purchased for $75 for Maryland residents and $100 for out-of-state residents. All passes must be clearly displayed within vehicles.
The National Park day-use areas include life-guarded beaches during the season at their “North Beach.” They also offer swimming at their “South Beach”, but there are no lifeguards there. Facilities include chemical toilets and cold showers. There are walking trails and sites for boat launch, clamming, crabbing, and fishing. National Park charges are $15.00 per carload per week.