Fresh edamame in McLean?
Frozen ones are available at almost every grocery store, even SuperTargets.
The out-of-pods are harder to find, but since you want in-pods...
I've seen them for sure at Wegmans and Whole Foods in Fair Lakes -- not sure how far you're willing to venture from McLean though. The Asian marts have them as well (Falls Church/Merrifield/Vienna/Fairfax areas)