Baby chicks infested with bird mites

[hikatz]

Where do you buy the diatomaceous earth, Del's never seems to have it in stock. how do you use it, can it be also be put outside or just used in dry areas.
A friend who lives in Hawaiian Acres, is also having a problem with stray chickens on her property, does not mind the chickens, except now she has a mites in the carport and house, and her dogs and cats are infected.