No disrespect to the others that posted..
Since you are VERY close tot he DC area, I would suggest that you contact the following organizations.
Based in Sterling, they are Porsche specialists, but have expanded beyond.
Ask for either Bill or Matthew. Tell them that Tom Newman referred you.
They are based in Manassas, VA. They build 80-90% of the local SCCA racer cages.
They are a little expensive, but the fit and finish are really incredible. You would never know that the cage didn't come standard with the car.
Mitch Piper built the cage for our Grand Am car.