If you think your GH3 camera needs and LCD View Finder, here's how Scott Pendleton modified the Carry Speed VF-3 LCD View Finder to fit [Thanks Scott]. Typically the GH3 body is too short, so you'll need to have the GH3 Battery Grip to start.
The next problem is that the GH3 battery grip relocates the tripod mount to the right (not centered). This causes a problem for the VF-3 not being able to shift far enough to the left to line up properly. Scott then grinded the alignment plate and drilled a new hole that will allow the Loupe to align properly. You can figure it out from the images below but keep in mind this will definitely void any product warranty.
Click any of the images (above) for a larger view. You can find the Carry Speed VF-3 LCD View finder at the CarrySpeed.com website (here).
Carry Speed VF-3 DSLR LCD View Finder with Quick Release
And if you're wondering what Eye Cushion Scott is using on the Carry Speed VF-3, it is specifically the Blue Star Oval Long (not oval large) found via B&H below
Blue Star Eye Cushion Oval Long for Carry Speed VF-3.