It moved!
I spoke with the owner before Christmas 2013 and they were just about to move. They're staying in McLean. I think they were moving to an historical and/or parks site.
Maybe... near Evans Farm. Maybe at the Claude Moore Colonial Farm? I can't remember the details.
But the owner is definitely keeping the business going. Perhaps you could contact him--the info is here
http://www.librarything.com/venue/24135/The-Old-Book-Company-of-McLean