Currently there are 11 native Telephoto Prime lenses for Panasonic GH3 and 7 of these lenses are autofocus (AF) type.
Panasonic GH3 doesn't have a sensor based image stabilization system but 3 of these Telephoto Prime lenses features optical image stabilization.
Since Panasonic GH3 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 4 Telephoto Prime lenses with Weather Sealings.