I've found my local wal-marts don't give out frosting buckets because it's against the rules (why only here?) but Sam's bakery has never turned us down, unless they didn't have any.
I personally wouldn't use a non-food-grade for food items even with a mylar bag but I do use them for non-food things, like matches, sewing supplies and so on.
Truly love my buckets! Actually time to get more. Got lots of dehydrating we'll be doing by the end of summer and I don't want to be hunting down buckets at the last minute.