The item is still there see
but it only shows compatibility up to the 2011 27in iMac, the 2012's are listed. This may be an over site or it may be that this doesn't work on the new models.
The plate was attached by removing the iMac stand so I'm not sure the change in the edge dimensions of the iMac should make a difference, the stand looks the same.
I would suggest contacting the store and asking.