Made by the Mamiya company for Sears this 1000 MX camera has it's own lens mount system.
This is the AUTO CS model.  Note where the shutter speeds are located,
on the outside of the lens mount.

 

Sears 2000ES
This seems like a more traditional 35mm. Not sure of the lens mount or
if Ricoh made this model.

 

Sears 500 MX TSL
This is a screw mount lens system.  I can only assume the shutter speeds only
go to 1/500 by the model number.