Currently there are 6 native Macro Prime lenses for Sony A7R III and 3 of these lenses are autofocus (AF) type.
A7R III also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on A7R III.
Since Sony A7R III has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 4 Macro Prime lenses with Weather Sealings.