From breeders. Hatcheries do not offer heritage, dual purpose breeds. They offer diluted, production-type forms of the breed. For example, an Orpington is a heritage breed. . . Hatcheries only offer skinny, small, typical looking Orpingtons good for egg laying.
Good sources for Orpingtons include Hinkjc, Steve_of_sands_poultry, and a couple others I can't remember the names of
Good sources for Plymouth Rocks include kathyinmo and several others. She also has true, purebred, dual purpose New Hampshires, too.
There are also several dedicated Buckeye, Delaware, Sussex, and Chantecler breeders on here too. All really good heritage breeds, you just need to find a reputable source. The Heritage Large Fowl thread on the breeds/genetics section has a lot of dedicated breeders there, even people like Chris09 who breed and raise the rare Rose-combed Rhode Island Reds.