Seek concentric punch set, new or used.  The only vendor I can find
is in Australia and will not ship to the USA.  Looking for center
punch of 2 mm, outer punch of 20 mm.  All other sizes okay.

Walt Gerber - The Antique Piano Shop

 [ For example, http://www.boehm.fr/concept.php?lang=en 
 [   twinnable and interchangeable circular hollow punches
 [ -- Robbie