Alright I was reading through forums and noticed how all these immune mobs give wep skill when you attack them, but blizz nerfed all of them. So I was thinking about the boss in shadowlabs which is immune until you kill warlocks. I don't know if this has been posted, i searched for it and nothing came up but this is what i did.
-Go to Shadow labs in auchindon (which is in terokkar forest)
-You should be level 80 to not aggro mobs
Make your way to room with boss #1, his name is ambassadow hellmaw.
Hug walls, etc so you wouldnt aggro mobs. Get behind hellmaw and attack him. This will level your wep skill and has been tested on retail server (also take off all your armor because for some reason you loose durability even though you don't get attacked). I got all my weps to 400. Have fun, keep it low!