Dumb Question About New Deadbolts

I'm a carpenter so I only deal with lock sets enough to screw something up occasionally, but a recent job made me curious...

My customer wanted a few deadbolts installed, but wanted them to be keyed differently (commercial application). She had a few Schlage deadbolts she purchased but they were keyed the same.

How do companies like Schlage key their deadbolts? Do they do a production run and have a big lot of product that are all keyed the same? Is it possible to purchase two Schlage deadbolts at the store that do not have the same key?