That's like saying "I bought a VW, how do I make it run like a porche?"
That said the broilers from hatcheries are from selected parent strains of white cornish and white rocks, several people are trying to breed up thier own, personsally I don't have time or space to keep 3 seperate flocks to make what I can order for $2 each. Some people decide to go with a large dual purpose strain instead.