I've published a 3D model of a GoPro mount that clamps around Blackbird Fabworx GT3 and Hard Dog "Hard Core" rollbars. It could work with other rollbars of similar OD of ~45mm. The mount is intended to have felt strips within the clamps to dampen vibrations and prevent marring of the rollbar powder coating or paint.
I hope you enjoy this model! https://www.printables.com/model/901313
If you prefer to purchase a mount, you may do so here: https://buymeacoffee.com/castillaricardo/e/262705