Other than the sources you've probably already found on the net using google, I'm not sure on what else there is. I know the barn owl trust UK has a bit of info on aivaries and care. It seems that in the US you can't keep owls, and i don't think anyone on here from the UK keeps any on here either. On the books front or other sources, I think there would be a bit more on captive care of birds of prey in general than specifically owls or barn owls. Is there a bird of prey keepers specific forum? I suppose a UK forum would be more useful in this case, but i could'nt find one.