aka Check valve for hydraulic valve lifter (11036-D4200).
This item has been unavailable for a long while AFAIK.
I was able to order two pieces of these from Humphris Oxford in the UK via their online store http://www.online-parts.co.uk/nissan...l#.U9PZ9LF9X0c.
It took a while because they had to order it from the Land of the Rising Sun
Perhaps one of our preferred suppliers here on the board wants to take some of these in store for easy distribution...