The Urban Angler is relocating to King Street in Old Town Alexandria. I think their still working on the building and they haven't reopened yet. I'd go to Orvis in Clarendon and talk with Dan or Trent, they'll push you in the right direction. If your looking for DC specific fly fishing you can't beat the Tidal Potomac Fly Rodders forum.
http://www.tpfr.org/
http://www.tpfr.org/