cap activated click pen kit?

[ArmyDoc]

I had a pen once that was similar to the Fisher Cap-o-matic in action, where instead of a button the end that looked like a cap was the button, and slid over the lowere barrel. Does anyone make a kit that works like this?

 

[Paul in OKC]

Long time ago there was a flat top American style pen that worked liked that. I tried a couple without much success. Not sure if anyone makes one now.