If you want cash flow, I think you will have to go further outside the beltway. Suggest you start looking in Frederick MD at the end of the I-270 corridor then expand your search to Hagerstown and Middletown. There are some foreclosures there that could cash flow if you buy right.
If you want to stay in Northern VA, then go to Centreville. Follow the Dulles Toll Road past Reston and start looking in bedroom communities where builders have inventories of unsold homes.
Areas off I-95 south of the Pentagon such as Woodbridge and Dale City used to be promising but even those areas are declining. You may have to go even further south to Fredericksburg and Quantico.