I have family in Northern VA and whenever I visit, I head over to Old Rag for a run. It will not prepare you for the altitude, but running up/down the Saddle Trail is somewhat similar to much of the Barr Trail in regard to gradient and technicality. The Ridge Trail is very fun as well, but is a bit more scrambly and less runnable. The vertical is 2,300, decent for your area. I am sure there are other good trails in that area. Good luck!