Food grade DE can easily be found on the internet. I purchased 50# from Earthworks Health on 3/7/12 (earthworkshealth.com). I bought the 50# bag because it was most cost effective. I shopped around and found they had the most reasonable shipping costs - otherwise it was pretty much a horse apiece for product price.
DE is (in my opinion) far better than borax for insect control. The bugs do not have to EAT DE in order for it to work, they merely need to walk through it. From what I read on various i-net sites, it takes approx 4 hours for it to dessicate the bugs.
I sprinkled the DE dust in all the corners of my house, behind furniture, on window sills, in closets & kitchen cupboards, etc. I've had spiders under the cabinet holding my parakeet's cage for a few years. I'd vacuum and think I got the little buggers, but in a day or two, the webs would be back. The day after I sprinkled the dust under & behind the cabinet, I vacuumed the webs (only, not the DE) and have not seen a spider or web ANYWHERE since 3/9/12! I bought an adjutant duster (a device to spray powders, not liquids) to spread the DE more easily. 'Sprayed' the garage and the spiders are GONE!
This is the time of year I start getting silverfish in my kitchen cabinets. I sprinkled dust in there, and so far, I have not had any of them. Will be heading to the attic next to get THOSE little beasties!
I do NOT work for Earthworks Health, and had not heard of them before. I can say that their prices are reasonable; they have an ENORMOUS amount of information on their website regarding uses for DE; excellent testimonials; and I ordered the product 3/7 - it arrived 3/9 - only 2 days lfrom NE to WI!!
DE is organic, toxin free, safe in/on/around pets and children, promotes health benefits taken internally (people & pets), kills head lice, bed bugs, mites, etc. and has been used by grain and livestock farmers for decades.
Hope this helped you!