Both starbucks.com and dunkindonuts.com have store locators. If you don't get many responses here, your best bet might be to search various cities along I-95 with the largest radius possible.
Dunkin Donuts are very very few and far between in the south. The only one I know of that used to be in Richmond isn't there any more and wasn't near I-95. Their website shows another in Richmond that's a little ways off I-95 and would be very out of the way if you wanted to take I-295 around the area.
Starbucks has a store near Virginia Center mall north of the city off I-95 (don't know if it's in the mall or outside) and one that looks like it's in a new Target in Mechanicsville off I-295.