I understand exactly what the OP is asking about.
Back in the original days of keyboard synthesizers, a company called Pratt-Reed ruled the OEM keyboard world. Everyone bought their keyboard assemblies from them, and they'd sell you single units of anything they made. Want one of the inverse color white-on-black style, five octaves (60 keys), created for a specific customer? No problem! Just say "I want the keyboard from the Moog XYZ" or whatever and they'd happily ship you one. An absolute boon to those of us who toyed with homebrew synths back in the day.
Alas, Pratt-Reed is no more. And as someone else noted, everything is MIDI now. That's good in some ways, bad in others.