The Bark River Mikro Slither easily fits a PSK. I thinned the scales down on one and it works very well in my AMK PSP. Adding a small Kydex sheath is no problem, IMHO, it beats the heck out of the scalpel in the kit. I tossed the scalpel when I added the Mikro Slither.
Getting a Blaze Orange Mikro Slither with hollow pins (to hold a lanyard) as a PSK knife is a good idea.