I think your best bet would be to go with a pen themed to emulate a K-bar. In order to accomplish this you'll need some thick brown leather and some thick black leather or at a minimum black dye or paint, a hole punch matching your preferred pen tube diameter, a clamp, and some slow setting epoxy. If your goal is a smooth CA finish (what my approach would be) you can just alternate one piece of black leather for every few brown. If the goal is to match the "feel" you could use brown leather and cut grooves while turning to then fill with black dye or paint, then soak the final product with thin CA and hit it with the buffer. May also require a little sanding if the CA blushes.
Either method, making the blank will be similar. You'll cut 3/4-1" squares, use the hole punch to match your tube and punch out the center of each square, soak both sides of the leather in epoxy and begin stacking the pieces onto the tube. Make sure there is a bit extra hanging off both ends of the tube so that when you clamp the ends together and compress it, it has room to "squish". You may want to plug the ends of the tube using a wax sheet if you have it.
I'm sure there are better tutorials of this method if you run a search on this forum, but that's the basics. Good luck