You can even do it yourself, it's not that hard.
I rekeyed a replacement cylinder for my '73 340 Duster so it matched the others.
You just remove the metal cap off the cylinder that holds the tumblers in place. File a tumbler (one at a time) until the key turns the cylinder, move on to the next tumbler, repeat until they all match the key, put the metal cap back on and install the cylinder in the car.
I even made a key for my '48 Dodge (filed a blank to fit my truck)