True, but hatcheries don't either. For any sexed chicks, there's 80% possibility that they are actually female, and 20% or so possibility that the sexing is incorrect and you have a male. [ETA the hatchery will tell you what the % are of the sexing being correct for the chickens you have your...
Now, if you're wanting to order day old chicks in a quantity of 6 chicks, almost any hatchery can help you, although there may be small order charges. Suggest visiting a farm store and getting them in person so you can skip the shipping and the wait.