Old paint codes are going to be challenging to have mixed properly with todays paint systems. If you have a good paint/bodyshop, they can possibly match the original paint on the car. They would be able to look up the original codes also. The code table may be posted here in the library section, I don't recall.
Otherwise, most of the Mustang parts vendors sell paint pre-mixed in spray cans, some sell it in quarts that can be sprayed with a gun.