AlDoori,
Indeed, there can be a long, long lag from when the last batch of a low volume, high end camera is produced and when supplies run out and it is officially discontinued. For example, Nikon announced the end of production of the F100 some years ago, but it is still available. My guess is that the Nikon F6 and Canon EOS-1V are in the same "undead" state, and several manual focus medium format bodies too. Also, a company might not make the final decision to not make a further run (and destroy the dies and tooling needed to do so) until the previous batch is sold out.
So maybe no RZ67 has been manufactured for years, but supplies still exist, and Mamiya has not yet made an official decision to never make any more.