If the Nikon 5T is hard to come by, then don't forget the Canon 500D, IF, the diameter of the Canon 500D suits the Nikon lens in question.
Unfortunately not all of the diameters available for the Canon 500D series of supplementary lenses will suit all Nikon lenses unless a stepup ring is used. The optical power of the Canon 500D is slightly weaker IIRC than for the Nikon 5T. The older Canon 250D is however stronger.