i've got an ultralight .692 bore gloss black back in autococker threads, good condition- has been used though. very slight wear on front milled shoulder (where front section screws in).
£20 + £3 postage?
Could do you a set of 3 gloss black backs (.684, standard, and the big .692) in a dye padded case for £45 + a fiver postage.
A.B