congratulations to this nice microscope. It was way ahead of it's time when it came out in 1934 and is still a good to use microscope today.
There was an external Köhler-lamp and a Köhler lamp-base (the "Brotdose"). These and other accessories turn up frequently on german ebay.
I can send you a german repair manual via e-Mail this evening if you send me you e-Mail adress.
Here is a bit to read on Zeiss Jena: https://www.mikroskop-online.de/Mikroskop%20Druckschriften.htm
The Zeiss Jena LG was also produced in Russia and later the boxy version of the Lomo Biolam was based upon it too.
It shares most accessories with the Lumipan, NF, NG. The nosepieces are exchangeable and 5-seat nosepieces are frequently available.
The nosepiece is simple to service, there are no ball bearings in it.
Heating the stand without optical parts to 60 °C will make disassembly much easier.