Easy Way to Remove E-Brake Cables Off Backing Plates

I'm looking for the plug to close off 1 of the holes in the rear backing plate on a 74 Duster. Plate has 2 holes, but 1 needed only for emergency brake cable. It's a 9/16 opening and no one has that size locally. Auto has assorted plugs, but not that size. Older plates had only 1 opening so could only use on right side and the other side had opposite for left side.