Dutch Valley specializes mainly in dry goods, not fresh foodstuffs. They do sell a grated Parmesan cheese but it won't be the Parmigiano-Reggiano. I would be surprised if you can't find the PM (the real thing) in Gaithersburg. I just don't know where.
Where you are physically located, I think you have two other reasonable choices but at much greater distances, Philadelphia or Pittsburgh. According to MapQuest, Myersville is located 160.52 miles from Philadelphia, or 2 hours and 51 minutes; it is 187.77 miles from Pittsburgh, or 3 hours and 8 minutes.
Philadelphia has several Italian markets that sell both Parmigiano-Reggiano and mozzarella cheeses, including some very good brands, and you should be able to satisfy your needs from such sources. Maybe one of our Philadelphia-based members can identify one or more such markets, including any that ship in the event you don't have a good reason to drive to Philadelphia.
The reason I mention Pittsburgh is because that is where PennMac is located. In my opinion, PennMac (at pennmac.com) has one of the broadest and best selections of cheeses and other pizza-related ingredients. I have bought the Reggiano-Parmigiano cheese from them before and it was very fresh and of high quality (and a reasonable price for the genuine PM). PennMac also carries the Grande mozzarella, Provolone, and other cheeses. If you are interested in canned tomatoes, PennMac carries the 6-in-1s, Stanislaus, and San Marzanos, among others. They also carry many of the flours that our members favor, such as All Trumps, Caputo Pizzeria 00, etc. PennMac ships but if you are in the area sometime your best bet may to be to load up on whatever pizza ingredients you need. You are much closer to PennMac than many of us, so you can do a cost comparison between driving to PennMac or having them ship.
PennMac's telephone number is 1-800-223-5928 (or 412-471-8330). If you call, you should ask for Rose. She is a member of the forum and deals frequently with our members and generally knows what they like in the way of pizza ingredients. The PennMac website groups pizza-related ingredients mainly in one place (look under the Pizza Makers tab to the top/right of the page) but there are many other products that are offered that don't show up on the website.So you should ask questions.