You probably will have to wander gun shows for grip dealers.
They did not work very well, one, for not being very transparent, and two, for only being a window into the window of the grip of the side of a magazine.
Clear and transparent plastics are some of the wort to work with, from the moulding and machining side.
You could be able to DIY a set, though. You'd need some RTV (Room Temperature Vulcanizing) mould-making compound. You'd need some clear casting resin, and a sample "smooth" grip to take a moulding of.
Note, the clear resins are very unpleasant for chemistry and smell. You will probably want a finishing kit with sanding pads that runs 800 to 2400 grit to get clear enough to see a photo through. Check out the folks at Micro=Mark tools online.