You can put in on the Md or VA side at great falls park. You need to pay by the day or get an annual pass. On the MD side you can run the fish ladder, falls, or put in at the bottom of fish ladder which is the top of Mathers gorge. On the VA side you can put in above or below the falls. On the MD side you can hike back up, paddle back up, set a car shuttle or bike shuttle.
There is also little falls closer to DC, its short and not as good as Great Falls or the runout below.
I think Luke Hopkins has a website called local paddler. He is from the area and you may be able to contact him via his website. I have to imagine that there is an east coast version of the buzz, it might be boatertalk.