May even try one with a target shelf on the bottom.
I'm trying to figure out if the palm shelf needs to be adjustable like the airgun blog did or just sized once with the right step.
This is probably Crosman's supplier:https://www.dbwebbinc.com/crosman-grips.html
I also used the overarm routing approach with a drill press, X/Y vise, and router bit. I scanned the grip frame and glued the printout to the wood with rubber cement to help locate the rebates and screw holes. Sculpting was done with a Dremel and 1/2" sanding drum, followed by pulling shop roll through under my thumb in the manner of a micro belt sander.
It's a homebrew aperture sight - all hardware store fare. The "eye cup" was an industrial suction cup in a former life. It's there to shield part of the target area and remove visual distractions. Works great for bulls eyes on paper, but target acquisition is kind of slow for anything else.