Reddit reviews Monoprice 100093 6-Feet PS/2 MDIN-6 Male to Female Cable (100093)

TBH, that is a very tough cable to find. In fact other than your link I couldn't find one anywhere, even on some sites that sell strictly MKB stuff. The Mimic cable actually looks to be pretty high quality so the pricing is the only reason I could see not to go with it. If you want a cheaper solution maybe get a ps/2 male to ps/2 female cable like this. That way at least it won't be sticking way out from your mobo's ps/2 input & putting that extra stress on it. Although it would give you alot more cable to manage unless you can find a really short one.

not only does it need the same plug, but also the same pinout and protocol.

this counts as proprietary hardware so nothing is guaranteed.

Might have found something here:

http://diykeyboard.wikidot.com/yamaha-triple-pedal-connector

They suggest you keep the sustain pedal you already have, and add simple on-off switches for the other ones. It's about $5 each for the switch, then you only need a cable with correct plug, and connect the wires to the switches.

As a DIY project it seems possible to do this under $20.

floor switch - https://www.amazon.com/dp/B01E0ZAMM6/

PS/2 extension cable - https://www.amazon.com/dp/B007TZCTEE/ (this I'm not sure of... PS/2 mouse actually only used 4 of the 6 pins, I think, so cables might not actually be fully equipped for 6-pin use)

everthing else is up to your soldering skills