I went to the ref CD and pulled up the production photo of Jeremy Bulloch wearing the suit from behind which has a great shot of the pistol in the holster shown here:

This weekend I was at one of my Dad's friend's house and he had several of his pistols out, one of which is a new .22 target pistol, the grip is what had my attention though in that it has the weighted rectangular bottom, anatomical grip with the finger overlay, and the grip continues into the body. Also because it's a target pistol the barrel starts just over the base of the thumb which is consistent with the picture but is not as long as the picture, but I think with some tweaking could work. I'm going to wait till the next gun show and see if I can pick up an uncut target grip without barrel and then give it a crack with a sander to see if I can make anything happen.