Skortzy...
The Kohler, Wisconsin Home Depot has Southdown - I just bought 4, 50 pound bags for $6.99 each on 4/9/2002.
The first store I checked didn't have any (green Bay), but they did a search on the sku (578-819)for me and found that the only HD in Wisconsin that had any was in Kohler.
They had 2 pallets, but one was marked sold. They said that they ordered 9 pallets last summer and will be ordering a new shipment soon since they are nearly out.
I can't wait to get my tank set up...the sand looks beautiful.