Welcome to the forum.

I have some experience with calf and ankle holsters and sheaths. IMHO the very best of them very soon become very uncomfortable. They also can hang up and hamper movement.

I'd love to know why you want to conceal your PSK beyond what would be achieved by kit(s) in a pocket. Surely such concealment wouldn't evade any search of your person.. and I have no idea why you'd want to do so. Why??

Consider: any inexpensive seamstress and many laundries can lengthen pants pockets. I've added about 4" depth for CCW carry, with no obvious visable changes. I've also "piggybacked" a pocket to the outside (thigh side)of the existing pocket. Drop your pants.. look at how the pocket is sewn in.. and imagine another one as a Siamese twin to the one already there. You have to unzip your fly to get to that pocket, but... well that's another story.

A clearer idea regarding exactly what you'll be trying to conceal may get you better suggestions.