I dug the colormaps out of GBA Doom II's rom file. Conveniently it has just enough levels to work in the original game, so have an eyesore:
I'm still trying to dig out the map data but I'm not having any luck. I have a few potential leads and I'm trying to map out what I can to make it easier to find without falling into unrelated data, but its elusive. I have no idea what format it could be stored in.