Currently there are 25 native Standard Prime lenses for Pentax K-3 and 18 of these lenses are autofocus (AF) type.
K-3 also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on K-3.
Since Pentax K-3 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 3 Standard Prime lenses with Weather Sealings.