My (2)local feed stores do not carry it, so I went to another a bit farther away. The girl behind the counter had not heard of 'food grade' DE, but went ahead and called their other store and found that they had a 50# bag in stock. Even there, they weren't sure about the food grade stuff, but a quick look at the bag will tell. It will say "Chemical Codex Food Grade". They were nice enough to have someone bring it over so that I would not have to drive even further. Now they will order it for me whenever I need it. My next thing to do is take the empty bag to my local feed store and see if they can start ordering it.
I always say befriending the feed store folks is always in your best interest!