There is supposedly a haftarah that even though printed in chumashim and assigned to a parsha that is actually never read
No. There is no Haftara commonly printed (excluding a mistaken edition, or something) that isn't used at least occasionally by some community. Note that some are used very, very rarely, which perhaps might lead someone to doubt if they are ever used.
Technically if there was a haftarah different from Shmini Atzeres (in Eretz Yisrael) or Simchas Torah (in the galus) assigned to V'zos Habrachah, then it would never be read. That would be since V'zos Habracha is never read on an individual Shabbas. However, I have never seen a reference to such a haftarah in any seforim or chumashim.
One could also consider what haftarah would have been read when the Torah was read in the tri-ennial cycle. I do not know what the minhag was for that cycle and none of them are printed in the single year cycle chumashim. They would therefore not apply as a possibility.
Note that What is the rarest Haftarah? gives the list of rarest haftarah.