I made an OM 4 grip which I 3D printed, I based it off the original, and it fits pretty well. I made this after seeing a post on a facebook group about how much these go for. I was fortunate enough to have two of these so I modeled a copy. I still need more practice with 3D design and with better programs to get better curves. I made this using a combination of flat bed scanning the part, tracing it in photoshop as a vector, and then building it tinkercad with digital calipers to get the exact dimensions.
It has the same vertical cutout for a section of camera leather for grip, but I may remove that to make a cleaner model and print with less supports. I also need to round out the top section. It currently uses supports, on for that section, the other for the screw hole. The model should be able to print without any supports though but I haven't tested it. It uses a small 3mm screw.