Where to Buy Vermiculite for Square Foot Gardening

One of the trials of Square Foot Gardeners is finding a source for Vermiculite.  I stumbled upon this Google Document with vermiculite sources listed by state.  There are none listed near me, but I did find one within easy driving distance for a relative who comes to visit.  I am looking into having them pick some up for me from Palmetto Vermiculite in South Carolina (or Coleman Farm Supply at 5980 Highway 101, Woodruff SC, (864) 476-2914).  Palmetto actually carries one specifically labeled for Square Foot Gardening.  Note:  looks like 2 cu ft = 10#.