How can I ground old 2-prong receptacles?  (120V)
The correct answer is that you cannot install a 3 prong grounded outlet without using a 2 conductor with a separate ground conductor, that's three conductors.  I know people cheat and put a wire from the ground screw of the outlet to the metal box and hope that the armor case is firmly connected to the box and grounded at the panel. This is not a good alternative to 14 or 12/2WG and can be potentially very dangerous. Example, if you were to have an open neutral, the ground can potentially take over, now you have current on the armor shield, not good.  Btw, there is no good way to remove paint from an outlet.  Just replace it. In your case, you should be looking at some new wiring.