Ideal Poultry has a policy of adding male chicks to small orders ("packing peanuts") rather than heat packs, unless you specifically request otherwise (you have to pay extra if you want a heat pack.) These are pretty reliably male, although of course they could mis-sex one.
Many other hatcheries require that you order a certain number of chicks, and they have boxes just the right size for that many chicks, so those hatcheries do not add extras as "packing peanuts."
It's common for many hatcheries that if you order 25 of one kind, they ship 26 (so if one dies in shipping, you still have the 25 you paid for.) If you order one each of many breeds, they typically do not add an extra of any of the breeds. For numbers in between, I've seen plenty of variation, both from one hatchery to another and sometimes between orders from the same hatchery.