Currently there are 21 native Telephoto Zoom lenses for Samsung GX-20 and all of these lenses are autofocus (AF) type.
GX-20 also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on GX-20.
Since Samsung GX-20 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 9 Telephoto Zoom lenses with Weather Sealings.