GTA V - MG42 Police Shootout on Vespucci Beach Alley (Lost MC vs. LSPD)

You can download this weapon model here: https://www.gta5-mods.com/weapons/mg-42-add-on-replace
It can be installed as an "add-on", without replacing in-game weapons, and you can buy it on Ammu-Nation, as well as spawn it with a trainer.