I know this first bit does not help you however a ZKK600 in 7x57 with the pop up peep was listed on used guns yesterday. Had a scope as well. It is already marked as deposit taken.

When I wanted a ZKK602 in 375 I put an ad in the Sporting Shooter magazine in the wanted section. I ended up with a couple of them, one with the peep and also a 7x57 which the guy who rang thought I might want anyway. It also had the peep. They are out there.

Rick