the Milkor MGL appears in Ready or Not has been confirmed already, but.....how about Small and Light Stand-alone type grenade launcher? (use non-lethal grenades only, of course)

https://i.redd.it/70jjexdg7cv21.jpg

a Small and single shot grenade launcher that can equip as a Secondary instead of Pistols. of course its Small and single shot so Milkor MGL launcher is more superior launcher, but when player want to use SMG/Carbine/Shotgun and grenade launcher both, i think Stand alone type grenade launcher is probably not bad.