Looks like it is for sale now – this ad on Barnstormers:

WWII LANCASTER GUN TURRET • ACCEPTING OFFERS • Very rare FN-4 or FN-20 Fraser & Nash 4 gun turret either from Lancaster or Sunderand missing cupola • PHOTOS HERE • Contact Tristan Masterson, Owner – located Bolwarra, NS Australia • Telephone: 0481308223 . • Posted April 24, 2016

or trade