i have a 1986 z31 and am looking for the part that the radiator cap locks too.

 

Try Steve Berman at 300ZXpartsforyou.com he is a specialist Z31 wrecker and he has lots of those obscure parts for these cars.

 

Or if that doesn't do it, locate the recyclers in your area at Car-Part.com--Used Auto Parts Market by searching for a common part and sorting the results by zip code. If you can locate a whole Z in your area it could be a real find for you. In-person hands-on is a great way to order used parts. Better prices, too, if you like to haggle.