There probably is a list out there but it is more likely you learn by just using and knowing about guns.
I did do one search and the first line that came up on Mec-Gar’s site says that if you own more than one gun you more than likely already use Mec-Gar magazines.
It is common knowledge among gun users that Mec-Gar makes nearly all original equipment mags.
I've done plenty of that and I have bought and used plenty of magazines for all types (and I've bought and used actual Mec-Gar magazines). Don't be so condescending. I probably have more than you.
Common knowledge is nothing more than 'lore' IMO. You positively asserted that they do make magazines for most of the manufacturers, so show me or tell me where I can find the "list."