Obviously Gears of War 2 did not come out on PC, but do achievements from Gears of War PC unlock the weapons skins as well?
Gold Sawed-off : Earned 'Commando' achievement in Gears of War 1
Chrome Lancer: Earn 'Don't Hate the Player' achievement in Gears of War
Chrome Retro Lancer: Earn 'Domination' achievement in Gears of War
Of course we already know about the Chrome Sawed-off, which is explicitly stated. This might be a hard question to answer though; Who has only played Gears 1 on PC and then decides to play Gears 3 on 360?