I tried all the feed stores in my area and none of them carried it in stock. I then called back and found one that would order it for me. It was 20 some dollars for a 50 lb. bag.
I am in West Springfield. I went to Westfield Feed today and they carry food grade DE...unfortunately they were out of stock. The guy said it was ordered and will probably be in by Mon. Easthampton feed is their sister store, so that might be an option too.