I dont know if this will help you but I have made friends with a commercial chicken farmer, he raises birds for large supermarkets, and they 'go' at 31 days, so I buy 80 or so then at approx £2 a time.
They are injected and mite free so thats all good
I keep them free range and add a bit more weight on them before we slaughter to eat.
Perhaps you could do this in Scotland to?