I found some more older PLC programming devices.
Very interesting keyboard on this Fanal Fanalog PU1262. And CRT display.
Octal in 2 rows. STOP, JA NEIN (Yes, no) and I think 4 arrows.
Fanalog 1251 is completely different
iF Design - FANALOG-Programmiergerät PU 1251
I found some old companies here.
Steuerungen / Hersteller aus vergangenen Zeiten =) | SPS-Forum - Automatisierung und Elektrotechnik
Another interesting one (not sure if octal) but programming via ladder diagram is the Telemecanique TSX T407. QWERTY keyboard and LCD display.
Interesting is also the Openplc Project to be used on Windows, Linux, Arduino, Raspberry Pi and some others.
The graphical programming languages (ladder diagram (German KOP) and function block (FUP, FBS)) will be converted. Some hardware seem cheap, but for a full system or a trainer it’s very expensive and only useful if someone really wants to use it.
There is also a PLC for the Z80 NDR computer. Even when not having that hardware, the software, descriptions and manuals are interesting (in German but with examples and comparison of ladder diagram and instructions.
But both are not in octal.