In Gears of War 3 for the Xbox 360, you can unlock the Golden Hammerburst as a weapon skin to use in the game.
The only way to get the Golden Hammerburst in Gears of War 3 is if you had it in Gears of War 2. If you had the weapon in GoW2, it will automatically come over to GoW3.
Check out my other guide for more unlockable weapon skins in Gears of War 3.