While it sounds as though there should be a market, I think you'll find that there are a few factors while will present problems, which is why there are so many free cockerels offered!
Firstly, if someone were to be able to sell them to the public, they would need licenced premises to process them. People with this kind of set up are unlikely to want your lovely corn fed hybrid birds as there is unlikely to be a lot of breast meat on them compared to commercial breeds.
We really enjoy eating our cockerels and they definitely taste better, but they do look rather scrawny compared to a supermarket bird. We have no specialist equipment and it takes us around an hour to pluck (or usually skin) and gut the bird, then you've got a bag of 'gubbins' to get rid of. So, while we are happy to eat ours, I would prefer to pay £4 for a supermarket chicken than go through the faf involved with unwanted cockerels.
Just my thoughts.