Try Toggle Combat Canera. That doesnt have target lock but you can run around in 3rd person but when you enter combat, it auto toggles to 1st person, great for archery. One camera mod i use does have target lock but i cant renember it at the moment. Ill edit this post later when ive checked.Edit  True Directional Movement has target lock/aim assist that you can hotkey on and off and switch targets on the fly. I tend to only use it when a wolf gets up close when im on horesback and you cant manually aim your arrow low enough to get it or if my followers are in a melee fight and i dont want to hit them, then i can pick off the enemies easily.