Have a MS 2000R analog synth. This is the one without the keyboard, that would be the MS 2000. What keyboard can I use to make it like an MS 2000?
Any keyboard with MIDI Out. Edit - The MS 2000R has a MIDI In port, yes? If so, all it needs is a keyboard with a MIDI Out port to control it. And a MIDI cable.
No such thing. The 2000R was designed for tabletop or rack mounting with no provision for attaching a keyboard. It is played via MIDI from an external MIDI controller. Any keyboard with MIDI will do the job.