Or make your own: https://tonnemansblog.wordpress.com/tenori-on-midi-cable-pin-layout/
Bax-shop.nl also has them, but not on the site, you can order them there. Most stores don't seem to have them. Which is kind of mind blowing to me. This cable being this hard to get ahold of and this expensive pretty much disqualifies the synth as a live instrument in my opinion.
(Apart from this issue and all the bugs I'm a major fan of the Reface series though)