Those were not used on EBs before 66 (nickel pup covers) and then by the time slotheads came out, the ring changed to be less a spacer and more of a mounting ring like regular geetar PAFs. That mounting ring design was carried through to the series IIs so there was only like 3-4 model years where that spacer could have been used. Never seen one for sale on it's own. It's just black plastic sheet though so super simple to repro with a handheld jigsaw;you don't even need an original as a template, just a mudbucker cover to trace.
