While not as huge as vinyl or cassettes, there is still interest in MiniDiscs and new albums are still released on the format.
- https://www.minidisc.wiki/releases/start?srt=%5Ereleases.dat...
- https://www.minidisc.wiki/releases/start?srt=%5Ereleases.dat...
In its heyday, there were a limited number of prerecorded releases, mostly from Sony. They didn't use M-O discs, and were pressed aluminum/plastic inside the shutter case, similar to a CD. They were supposedly much cheaper per-unit, but with a high setup cost.
I still have a handful of the prerecorded ones. My favorite is Pink Floyd's _Delicate Sound of Thunder_, which was two MDs in a special dual case that fit no storage system ever imaginable. Just looked these up on eBay, and I think I figured out my retirement plan.