My dogs used to have flaky skin too until I switched them over to Nutro Ultra. That by itself got rid of dry skin and gave their coats a beautiful shine.

There is one product called Hair of the Dog

http://www.docsblend.com/H-Info.html

I've heard some pretty good things about.

And regarding puppy mange (demodectic mange), I had to go through that with my GSD. The vet prescribed Ivermectin which I gave to her every other day. What I also did was put some vasoline on her nose (which is where the mites were and the hair was coming off and skin was flaky). The vasoline helped by smothering the mites and providing some moisture and oils to her skin.