[Pahaska]

You need a "real" lock shop. Our city has only one shop (Cothran's) that can reliably do more than simply duplicate keys. They can also make a key if you take them the lock itself in most cases. They either pull the cylinder, measure, and cut a key to fit the existing tumblers or they simply put in new tumblers and cut a key to fit the new pattern.

Cheapest approach of all may be to simply buy and install a new cylinder in the existing lock. There are some other threads that have cylinder part numbers.