Cluckin tractor - Have you tried looking at the vetshopaustralia site. They seem to have lots of products on there suitable for caged birds to counteract fleas, lice etc.. I find them very cheap and buy all my dogs flea and worm stuff from them and they cost me half what the vet tends to charge. That Pestene powder has gone up again to $17.50 at a few places (perhaps they have cottoned on to the fact that a lot more people are starting to keep backyard chickens!)
Also my breeder who supplied me with most of my Silkies recommends spraying the birds with a low irritant fly and mossie spray. He said to just make sure you cover their faces and give them a quick spray. He has been breeding Silkies and other poultry for 50 yrs+ and he gave me a basic facts sheet on health care of chickens etc.
I must admit I haven't had any problems with lice etc and I am always checking the girls - perhaps their dust baths are doing the trick.