The G6 Commando is used by the UFE in Max Payne 3 and is not found anywhere else.
You can find all the golden pieces of the G6 Commando in A Fat Bald Dude With A Bad Temper. The golden pieces will increase said weapons magazine capacity by 10 rounds, bringing the total up to 40 rounds per magazine. The magazine will also change into a dual drum mag.
- Max Payne 3