I'm sure you've considered it, but wouldn't milling aluminum down work in this case? There's only the two angled surfaces that have to exactly match the existing. The rest just has to meet a couple functional standards (screw head recessed enough to not interfere with the tripod plate). I'm interested to hear why you are thinking of 3d printing instead.

FYI, the screw itself should be easy to source. I actually have a spare since I needed a stronger one as the attaching point for my camera strap.