Deb, we did Mt Rushmore last September, and I got some help with quilt shops from folks on another quilting site: Rapid City has the Quilt Connection; Heartsong quilts in Hot Springs; there's a really nice one on the main street in Hill City (I can't recall the name.) These were all very nice places.
Hope you enjoy your trip. We loved everything there, but were especially impressed by our trip through the badlands. I really enjoyed going through Custer State Park, too.