Ignition/Steering Column Problem

After dropping my child off at school, I went to park and shut off the engine. The key free spun and would not shut off the engine. I ended up shutting down the engine by pulling a fuse and disconnecting the battery since the radio stayed on. After some googling, it sounded like the ignition lock cylinder had broken. I removed that and it seemed fine. After putting it back in and as I was turning the key I can see a plastic looking rod sliding up and down. Looking down the steering column I can see a little hole a few inches down and when the key is in the on position I see the continuation of this rod, But when I turn the key off, I see an end of the rod and disappears as I continue to turn the key off. What is the name of this plastic rod and is it possible to replace it? Thanks.