Wiring harnesses to replace yours are available at AAW (American Auto Wire). You do not normally just splice in wiring for the windows as they are all bundled into a harness. You could unwrap the original factory harness and splice in the wires you wanted but if it were me a replacement harness is much less labor intensive.
The switches are going to be more difficult to find. You can look for them on restoration houses, just do not limit yourself to a Chevy as electric windows where standard equipment on a Caddy or Buick, possibly even the Olds 98 and maybe the 88. Once you find the actual switches you then need to find a used arm rest for power windows for all four doors. Once again look beyond a Chevy, as the arm rests are all the same, even though the door panels differ.