I don't know much about silkies, but can they be free ranged in the same way Vanakrishna says? Sounds like gamefowl / semi-feral breeds rather than silkies. They have very different feathers than most chickens, and may need special care. I'm not sure, not an expert.
I've seen lots of people suggest that the best protection from coccidiosis is putting a pan of dirt in the brooder, or just brooding outside.
For organic feed, sadly lots of organic feed doesn't have proper amino acid levels when compared to non-organic. I started feeding organic at first for the same motivations as you, but I decided to just get a commercial feed that gives them what they need now. They don't 100% feed themselves because they're all dual purpose or layer breeds, but I do see my fayoumi hen catch beetles out of the air and chow down, so she's at least supplementing herself with that. I'm out rural though, and have bugs aplenty. They're still cheap eaters though.