Auto or Manual shift? The guts of the columns are a bit different.
Hopefully, all you'll need to replace is the cylinder. The good news is the cylinders are available at most auto parts stores (Dorman Brand), GM dealers, Rock Auto, Summit racing, and others. They're not super expensive $20-$40 depending on finish. The bad news is you may have jammed or broken the switch actuator rack and selector. This is what the key cylinder turns to operate the switch inside the column and IIRC they are pot metal.
No matter what, you're going to have to remove the steering wheel, the lock plate, and turn signal switch to get to the screw that holds in the lock cylinder. If you don't have one, buy a steering lock compressor to make it easier to remove the lock plate. Well worth the ten buck cost. When you get the cylinder out you should be able to see if it's a jammed cylinder (fingers crossed) or not. If the cylinder is jammed, you can try using a regular screw driver in the switch actuator and turning it to start the car. If the actuator turns and starts then the actuator rack and selector should be good to go.
Final Recommendation: Look around on the site or the WWW and get a PDF copy of the service manual for your car. Section 3.3 has possible causes for the lock not to operate. Sections 3B4 and 3B5 has disassembly instructions for the steering column and switches.
[This message has been edited by Mike in Sydney (edited 06-08-2021).]