Yes, here's the link to a manufacturer:
http://www.elmers.com/Products/ProductDetail.aspx?item=1065§ionid=3&catid=27#
The sandbags come in a plastic container, and you do have to do a little bit of shaping to finish them for display. But they look really good when finished.
Prost!
Brad
Rob, this was intended as a tongue-in-cheek tip that you can make them yourself, if you'd like, so I hope it didn't offend. I got the tip about Elmer's from Shep Paine's diorama sheets in the Monogram armor kits, back in the day. I have used it to make scale burlap bags, as well as a gap filler on some figures.