Where can i find a store that sell rock hammer and other geology equipment within Northern Virginia?
I can't give you an exact answer, because it has be a long time since I did any rockhounding. However, I have a couple of suggestions.
The Northern Virginia Mineral Club meets on the 4th Monday of every month at the Long Branch Nature Center, 625 Carlin Springs Road, surrounded by Arlington. Phone (703) 228-6535. Someone there will certainly know the best places to acquire supplies. This being the 21st Century, they also now own a Web page: http://www.mineralclub.org/index.html
George Mason offers a major contained by geology, which means that there are lots of population there who need geology equipment. I would bet that the GMU bookstore sell what you need. You could call the Geology Department department and ask: (703) 993-1642.