He's restoring the full terminal, not just the keyboard. From what I can
read, the Wyse 50 uses an unusual 10-pin DIN connector and I suppose it would not be easy to find the pinout either.
Wyse's keyboards from this era are otherwise sturdy and well made. Some of them have thick double-shot keys in DCS profile even. I would clean that though, and possibly retr0bright it.
@kharma: You'd be looking the F15 keycap. The Break key's keycap is in its position.

I know a lot of these keyboards have been scavenged for keycaps and/or switches.