First thing first, a good paint job could easily set you back 10 times the value of your Canon P, so you'll have to ask yourself is it really worth it or is it cheaper to get one of those original black paint Canon P!
Anycase, in order to repaint, the origin paintwork has to be removed, sandblasting is one of the ways to achieve a nice smooth even profile before coating of the black paint can be done, if I'm not wrong, should be more than one coat too!