There is an Italian/Gourmet market in Bethesda called, I believe, "Cornucopia". It has a nice selection of Italian foods, although the prices are a bit on the high side.
The proprietor does stock small bags of Caputo flour (approx 5 pounds, I think). I don't believe it is the Pizza flour, but the proprietor indicated that it makes a great pizza. I have not yet tried it. The store is located on Norfalk avenue.
Good luck and please let us know if you try it and how it works out.