Reader Question: Mid-Century Door Knob Parts

Penni wrote me recently and asked:

I am looking for the rosette and door knob guts for these glass/crystal Schlage door knobs. Please help.

I wrote Penni back and let her know a few things: 1) I have no idea where she could find replacement parts for these knobs 2) Having tried to find replacement parts for my own mid-century door knobs, I know they can be nearly impossible to track down and 3) I would still do my best to help.

So this is my call for help. Does anyone know where to find replacement parts for mid-century door knobs?