many ant powders for sale here contain permethrin, which is the active ingredient you need, and are much more widely available than powders that are marketed for dealing with mites/chickens - you can even find them in some supermarkets, for example.Thanks for the links...I'd seen the Amazon one. I'll search around and get something asap so that I can actually be doing something helpful.
Thank you very much
Good luck with your battle with mites.