Capcom over the years has had a ROM set you could buy on and off. Not sure if they still do. Think it was side by side with an arcade controller. I think there is one of their current console releases where there are a bunch of games and it uses MAME as the core to run their games. They are the only one I can think of that has sold ROMs to be used in MAME both loose and bundled. There was a service about 20 years ago claiming they had the ability to sell them but it seemed kind of shady. Also it is not very clear cut on many of them anymore who actually owns the game. Most of it has very clear lineage but not all of it.
Jamie Fenton has released the ROMs for Robby Roto as freeware. So that's one.