I found a source of supply in Baltimore just last weekend while I was visiting my brother. It's Prima Foods at 51 Kane Street, Baltimore, MD 21224. They're a food distributor, but they also have a retail store at their distribution center. The retail shop is small and focused on Greek foods, but they have a service window where you can request other items from their warehouse stock. I asked if they carried General Mills' All Trumps flour and they were more than happy to sell me a 50lb. bag for about $18.00. If you Google the name, you'll find that they have an extensive (but non-exhaustive) product listing online. I'd post a direct link to their site, but I'm a new user on Pizza Making and can't post links yet.
Prima is located right off I-95. Their website provides the following directions for people approaching from the south:
* Take I-95 North towards north Baltimore
* Take the Eastern Ave exit 59 - go 0.3 mi
* Turn left at Eastern Ave - go 0.3 mi
* Turn right at Kane St - go 0.7 mi
You can call them at (410) 633-5500. The retail store is open 8-5 M-F and 9-1 on Saturdays.
You might also be interested to know that Wegmans Supermarket just started carrying DOP-certified San Marzano tomatoes. Wegmans is based in New York State (where I live), but they have a store in Virginia at 14801 Dining Way, Woodbridge, VA 22191.