Currently there are 6 native Wideangle Fisheye Prime lenses for Panasonic GH4 and 2 of these lenses are autofocus (AF) type.
Panasonic GH4 doesn't have a sensor based image stabilization system and none of these lenses have optical Image Stabilization.
Since Panasonic GH4 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 1 Wideangle Fisheye Prime lenses with Weather Sealings.