If you have the need for a Virb to GoPro adapter and don't want to buy a whole set of mounts. You have or have access to a 3D printer. I have posted the print files for a version of the same. It uses the Virb thumbscrew and an M4 acorn nut or M4 nylon insert lock nut on the Garmin side and the standard GoPro style thumbscrew on the other.
Virb to GoPro Mount Adapter on YouMagine
Virb to GoPro Mount Adapter on Thingiverse
Just my way of saying thanks.