The S had a rather short production run, resulting in less than 5000 units being made. It can be very hard to find any of the original Asahi cameras, but the S is rarest of them all. Here are my 2 copies of the S in black.
Pentax SBlack Pentax S.1958 Pentax SAsahi Pentax SBlack PentaxBlack Pentax ScrewmountPentax Screwmount
From Asahi Pentax - AP, S and K models