A linisher with a fine belt on it would be the best thing to "sharpen" KO punches.
Bear in mind, that you can wreck a decent metal tool by over-heating it, making it soft (ie: ruining the temper on it).
Have water on hand and keep the tool cool, doing a wee bit at a time.
And putting the wrong angle on cutting surfaces, will render a tool useless, if you don't know what them angles are, it's best to get professional folk to do the work for you.
You wouldn't get an Architect to do your electrical work, so on the same side of the coin, electricians are not tool sharpeners.
I'm lucky I suppose, I had a background in mechanical engineering/fitting before I was ever an electrician, sharpening drill-bits and what-ever is second nature to me.
Save your money and get a pro to do it, that is what they are good at.