Londontowne Tropicals in Edgewater is another option. I saw on their Facebook page they recently got Lemon oscars. They also usually have assorted varieties.
Beltway Aquarium in Waldorf MD. They specialize in SA, AF, and CA cichlids...flowerhorns, Pacus. Even had giant loaches awhile back. Great fish but the manager/owner is tough to deal with.