My buddies 182 is in the interior shop right now, he told me that was one of the upgrades he wanted done. He seemed to think the wiring was already there? I will find out when he get's it back.
Do you have the interior rear dome lights? There should be a switch on the pilot's-side aft door post that turns on the back seat lights. The underwing lights are wired in parallel to these. So while I doubt the wiring is already in place, it should be super easy to just run a single wire from the interior lights out to the inspection hole on each side. I'd call the wrecking yards for parts. It's just a lamp holder and a bent aluminum reflector behind it. The inspection cover has a square hole cut in it with a piece of thin plexiglass. You could almost owner-produce these parts if you had a willing A&P.
I just ordered some off of eBay. I'll strip, prime and paint them, and get the IA to wire them up. The plane is all pulled apart for upgrades and an annual as it is.