Currently there are 48 native Wideangle Prime lenses for Canon 5D MIII and 24 of these lenses are autofocus (AF) type.
Canon 5D MIII doesn't have a sensor based image stabilization system but 4 of these Wideangle Prime lenses features optical image stabilization.
Since Canon 5D MIII has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 12 Wideangle Prime lenses with Weather Sealings.