These are not rare, or even what I would term scarce, but definitely sought after and not easy to find.
In my observations (not scientific but tiring
) there seems to have been a fairly large proportion of nickel 2" 15s produced, relative to blue ones. At least they come up for sale - perhaps the blue ones don't? $550 is a good price for one with the box, so slightly worn finish, no box and replacement stocks may go for slightly less. Good luck in your decision.