I thought you were trying to use the vertical.ini in the traditional sense, not as info to feed a script etc.
MAME File Manager…
…should be able to generate a list of vertical games. It can also move your roms for you.
I also don’t think it is limited to MAME rom sets but it has been years since I gave it a spin.
This looks like just what I need, but it requires a data set and it doesn’t look like he has updated it in years (2018). I couldn’t find one anyway.
Has it been that long? I’m not surprised I guess… there was some drama in the scene around that time. I’ll poke around and see if I find any signs of life.
Edit. I contacted the author… we’ll see what happens.