The un-interesting part of the bike handlebar mount of my cheap GoPro-lookalike broke, and so I reverse-engineered it and made a customizable model from it. You can either print it out as-is (which is probably GoPro-compatible), or mess around in the SCAD file - all parameters are customizable.

This is a quick and dirty project - I bet it could have been done better, but here it is for you to use or modify.