At a year old, you'd get very little for them, as they're way to tough by now for anything but stewing, like in a crock pot. So unless you have lots of them, (hundreds?) you'd be better served to put them in your own freezer, and crock pot them as needed, use the meat for any tasty dish you'd use cooked chicken meat for. You can also pressure can them, I'd be very surprised if any meat remained tough after pressure canning.
When selling chickens commercially for meat, I think you would have to make arrangements beforehand with a company to buy them from you once they're market size. A grocery store doesn't buy from individuals, and certainly not year-old birds.
In most states, even selling directly to the public, you must have your birds processed by an approved facility, and that costs anywhere up to $4 per bird, depending on your location.
