this guy is using a transmitter with his minidisc, im sure any transmitter you could find would work
seems like kind of a chore having to charge 3 separate things though. if someone would just do a kickstarter for a new minidisc player that had bluetooth built in and usb-c to power it i would buy one in an instant!
the minidisc i have now uses mini usb to transfer data and then has a weird 3v charging port, and the cable for that doesnt work anymore so im just stuck with using AA batteries to power it now. its a bit of a mess. these days it would be just a single usb-c port that would handle all that
good luck with your minidisk journey anyway if you head down that road haha
ah ok! i have a fiio btr3 bluetooth receiver that is something along those lines. it doesnt show any track info but its got buttons at least and you can plug in whatever headphones you want. there could be others around that are more like the MD remotes but i havnt done much research
if youre on android theres also “key mapper” by sds100 that will let you change to the next/prev track by long pressing the volume keys so you dont need to take it out of your pocket!