I did a Google search for 'dry ice near california, md', and came up with nothing more local than Waldorf. However, from reading thru some of the listings, it looks like some beer distributors carry dry ice. Might be worth a call to a few locals, like Guy Distributing or something.
The Food Lion near my folk's house in VA had a small bin of dry ice for sale inside the store. I don't think they have it anymore tho, maybe only during the heat of the summer.
How much do you need? Got a CO2 extinguisher? Blast it thru a cloth and capture some.