You may also find someone at the International Dyslexia Association's referral list (interdys.org). These specialists have more training than a 'writing coach' and a different kind of training than typical classroom teachers. In Fairfax County, you can also have a look at FCPS's tutor list which lists teachers who tutor on the side.
http://www.fcps.edu/cco/prc/resources/documents/PRCTutorListJUNE2012.pdf. MoCo may have a similar referral list.

Stixrud in Silver Spring (Stixrudtutoring.com) has a list of coaches they train; the list includes their area(s) of expertise. They work in various places around the region. While I don't have firsthand experience, I know a couple of people who have used them and were very pleased. Good luck!

I too would be interested in finding one in Reston/Herndon area...

My ds is 8 years old, is finishing 2nd grade. He has ADHD. He is a reluctant reader and writer.
All he want to read is prehistoric animals, dinosaurs, deep sea fishes.
He has been struggling in writing in classroom.
I would like to find a writing coach who can work with him during the summer.
Please help to recommend one who has experience working with adhd kids. We live in Montgomery County.

Thanks a million!