It seems like the common solution to holster a (usually toy) PKE meter is to buy and modify a holster for a measuring tape. I wanted something that evoked the original belt gizmo and trap holster, so I set out to design and build a custom PKE holster from leather.
After watching some how-to-videos on working with leather I made my way to Tandy Leather out by the Portland Airport. I found a scrap piece that was large enough for my design (though a little thicker than I wanted). Kudos to the manager there who gave me a deal on the piece (around $20 IIRC) and offered helpful advice.
I mocked up my prototype from old cereal boxes, making sure both my 1989 PKE meter and newer, more-accurate PKE could comfortably fit. I used this to guide cutting out the leather. I built a form from plywood, soaked the leather, and clamped it to the form to hold the shape.
I dyed the pieces black and applied Super Sheen. I glued the pieces together with E6000 glue.
As my leather parts were a bit too thick to accommodate both parts of the snaps I ran small screws though the leather and into the hollow shafts of the snaps, secured with glue, to strengthen those attachment points.
I glued some felt to the interior to mitigate the leather scraping my scratch-built PKE meters.