A spectrograph definitely needs a reference lamp.
As a minimum a Neon, this provides calibration around Ha which is an important wavelength for astronomers. The RELCO is also good and give a wider coverage.
When I started with the Spectra-L200 "IKEA" kit, I had the same reference lamp issues.....
I found at the time that the hand held fluoro "inspection" lamps had a small 12V to 110/220V inverter built in, so I used to raid the hardware shops and buy them up, and strip them for the inverter and the 12V plug.
The inverter looked very similar to this one:
https://www.banggood.com/150W-Inverter-Boost-Module-150W-DC12V-Step-Up-Board-Frequency-Square-Wave-p-1278570.html?rmmds=detail-left-hotproducts__3&cur_warehouse=CN
This initially powered a neon lamp. I used about 100 of them (!!) with no failures, no issues, in fact I'm still using one of the early build inverter/ neon set-ups today, almost ten years later.
This is shown in "Astronomical Spectroscopy for Amateurs" p160 and p202. There's also a "non commercial" circuit diagram for a suitable inverter.