Complete list at http://www.royrogersrestaurants.com/locations/
The most authentic (just as outstanding as you remember them from the 1970s-80s) Roy Rogers are in Eastern Fairfax County at Manchester Lakes (Rt 7900, Franconia Springfield Parkway and Beulah), Woodlawn/Mt Vernon (US Route 1, Old Mill Rd, Mt Vernon Memorial Highway), and Belle Haven (Bellview Blvd). Same outstanding food, original BBQ sauce, Fixin' Bar and great service/friendly staff just like you remember. Highly recommended!!!
There are others owned by different remaining franchisees, including several in Leesburg VA/Frederick MD (pretty good, but not quite as good as the Eastern Fairfax County restaurants), and of course those of the "NJ turnpike" variety that give the Roy's legacy a bad name (generally overpriced, mediocre quality and mediocre service).