I’m using MAME 2016 and was wondering where the ini file was
Just stumbled across this post. I know it’s old, but I think it is in the …bios/mame2016/ini folder on Retropie and In the Retroarch/mame2016/ini (or something close to that). Best bet if you run into this, I think, is load a game press Escape key and look in the Mame menu for the ini path setting.
Hope this helps someone.