By the "key barrel part", do you mean the entire ignition switch or the rotating keyed element
within the ignition switch?
Replacing the full ignition switch was a simple exercise when I did my '81. A PO had sorta-kinda ghetto-rigged an ignition switch from a riding lawn mower. Gag me! Plus a key was broken off in the seat lock and the fuel cap lock was full of epoxy. I'm thinking angry ex-girlfriend.

The trick was locating the proper terminal/wire match up. Shop manual solved that. Suggest if you're replacing the entire unit, snap a few digi photos to remind yourself of which wire goes where. I usually do a quick pencil sketch.
If you're asking about the lock itself, a locksmith
might be the person to see.