There was never an adapter for hanging lenses in Exakta mount in front of a Nikon. It makes no sense. Exakta register is shorter than Nikon register.
I've hung one lens in Exakta mount in front of a Nikon. 135/2.8 Steinheil Auto Makro Quinar. I used two Novoflex adapters, LEIEX and NIKLEI-K, each 6 mm +/- thick. The lens as adapted's far focusing distance was ~ 1m. Fine for closeup work, otherwise useless.
If you want to use lenses in Exakta mount (why?) get an Exakta or Topcon RE body. Forget the Exakta body, get a Topcon.