USAJOBS - The Federal Government's Official Jobs Site - Fed's Job Listing Site. Go here first and do a search on those areas you listed above and see what comes out.
There are various Federal Government contractors and subcontractors that you should look into, as they will be a bit easier to navigate and get your foot in the door. Here is a list off the top of my head:
CSC, Lockheed Martin, Northrop Grumman, NetStar1, General Dynamics, SAIC, Raytheon, Booz Allen Hamilton, CACI
Go to their websites and look at the job openings in the NOVA area and apply for what you think you can do. And while it's not direct Federal Government work, if you get onto a contract, there is always the possibility that you get selected to be plucked from the contract to work directly for the government.
The company I work for hired me to work on a DoD contract, and I'm now getting transitioned to do work on a contract for USCIS. And while I will not have the direct contact with the client like I did when I worked for DoD, I love working for my company and they've taken very good care of me.