I know a handful of mafia/action fics, but not many of them are OT12/various pairings.
spy!AUs are pretty full of action, and some of the ones that I like would be Endgame by fumerie and a dance of falling stars by canttakeabreath. I do admit that I prefer the latter more, but both are still excellent reads if you’re looking for action.
135 Seoul by changdictator does have loads of action, too, and may be what you’re looking for, really.
While it isn’t a mafia fic, Murder In a House of Angels by lunathunderhead may appeal to you as well. It has some action in it, although I’m not quite as fond of this fic as the other three that I have mentioned above.