Leitz Auction has this rare Nikkor-N 1.1/50mm in their upcoming auction that will take place on June 10 in Germany:
“Nikon was the first of the major camera manufacturers to offer an ultra-fast 50mm lens. The famous Nikkor-N 1.1/50mm was an impressive optical achievement, with the lens containing 9 optical elements in a relatively compact housing. A rare version of this special lens, in M39 mount and with a black front rim will be available in our June auction.”