Hard to believe or not they will. I was entertaining the idea of selling White legbar eggs to a hatchery. I am NPIP so I can do this. They wanted 1,000 eggs at a time. I could not do this, during the time of the year they wanted them.
Living in Minnesota made shipping them a problem. I only had around 20 White legbar hens, 1,000 eggs would have taken me too long to accumulate also. BUT they would have bought them.
That is how most your heritage breeds and rare breeds are obtained. There are some places that have their own flocks, but most do not. They are hatcheries.
I am not saying you will get the best birds from a hatchery. Any breeder that shows will keep his best matches to themselves. BUT that said, if a chicken lays 150 eggs during hatching season are you really going to hatch them all?
No breeder hatches every egg from every hen all season long. I "as do most others" hatch a number that will produce enough to pick from for future breeders. Roughly 30-40 chicks per breed and about 20% will go on to be breeders. Then the excess eggs get eaten just like everybody else's eggs do.