so my old ignition key broke off in the ignition lock cylinder last winter. i was still able to start the car since the key part was stuck in the cylinder, but today i thought i found a spare and decided to dig the old piece of key out. well i got it out and found that what i thought was the spare was actually for my old TSTE

then i tried sticking the piece of key back in the lock cylinder but it doesn't work so now i can't even start the car. the steering column is from a '93 Lumina that came from the j/y so i can't just go to the GM dealership with my title/VIN and have them cut me a new one (if they could even do that).
so....i gotta replace the ignition lock cylinder. i have a steering wheel puller but what else do i need to do? i haven't actually replaced a lock cylinder in a W-body before. hopefully a new lock cylinder isn't too expensive. i'm assuming NAPA would have one?
TIA