I can 2nd Stage III Concepts -
I am only familiar with the 1st iteration of PC from a few years ago.
I know Brian of AAudio Imports came out w/ the 2nd generation and looks like a 3rd generation is on the way in 2017.
It is rumored that china is buying a good portion of these PC, it would explain the absence in the secondary/ used market. Also of interest would be noting wether or not these designs are showing up in the "gray" market via china?