Those came off the 1982 and 1983 T-Type regals with the N78 wheel option.
Complete caps are still available from gbody parts for about $89 a pop if I remember correctly. Added bonus, that same chrome cap with the 86-87 black and silver style center would be of a similar type as the 1982 GN. Could swap the disks between the two and possibly find a taker who needs a spare set for their 82 GN...