Here is an example of the type of chemical insecticide I use in my barn. I get mine at the local farm store, so I assume it's available in your area as well. Anyway, click on this if you are interested.
http://www.bugpage.com/pyrethrin.php
Yardegg
I think everyone who keeps chickens long enough will eventually get ectoparasites like mites, lice, etc. I've had a real problem with my feather-legged breeds like Buff Brahma Bantams. So much so that I have all but phased them out of my coop in favor of Wyandotte Bantams (a clean legged...