Harry, the other best option might just be to pour the plaster and then carve your own cobblestones . . . it'll be tedious work, but it would probably go faster than you think.
John, you too, you gotta make contact with those folks over at the Magic City Car Modelers:
Trussville public library
201 Parkway Drive
Trussville, AL 35173
Telephone: 205.655.2022
Cool beans, Patrik . . . keep it going.
And Rob, I find that these vehicles really look amazing with a bit of camo and a number or some sort of insignia . . . it formalizes their credibility, I think.
It's all good, it's all good eye candy!