Pentax has given their cameras many names on models and series. One of the first was the Asahi Pentax K. That letter has been coming back.
We hereby present: Asahi Pentax K, Asahi Pentax K2 and Ricoh Pentax K-3:
Read and see more of Asahi Pentax K at Asahi 1952-1964
Read and see more of Asahi Pentax K2 at Pentax
Read and see more of Ricoh Pentax K-3 at Pentax K-:2009-13
The official producer was Chinon, according to Alpa sources. But we know that Cosina produced some cameras (and lenses) for Chinon.
The ALPA 2000 was a Cosina with M42 mount. I used to own one. Ever wonder why there are ALPA badged M42 lenses on eBay? They are from Cosina too.
Sadly not found the Ricoh XR-7 / Sigma SA-1 / Sears KS-2 camera(s) on the site. They could be produced by Cosina as well, but I have no information about this.
For an explanation of the penta mirror, please see the page "Some Definitions".My definition of PP SLR also include the penta mirror cameras.