My experience in building and using a 20-note John Smith roll punch was
described in a COAA Carousel Organ magazine article which is reprinted at

http://www.wallace-venable.name/mechanical-music/Hand-Punching%20My%20Own%20Rolls%20from%20Midboek%20Templates,%20Venable.pdf 

Jonathan Holmes asked about a circular punch and die for keyless music
for a Wilhelm Bruder Söhne Model 77 which has holes at 3.5 mm centres.
He was advised the punch needs to be 3.2 mm, and asked about materials.

I have had decent results using oil hardening steel rod and strip stock.
As far as I know, 3.2 mm diameter is not a standard rod size, but it is
about 0.126 inch which is close to 1/8 inch.

In the USA, ENCO sells 1/8-inch oil hardening drill rods 36 inches long
for $1.54, which is roughly 1.25 UK pound per meter.  Even if you have
to import it a lifetime supply is not expensive.

http://www.use-enco.com/CGI/INPDFF?PMPAGE=899&PMITEM=409-0005 

I would suggest basing the design on a 1/8-inch punch.

Jonathan said "Being a circular punch for keyless music the punch, even
though it is a foot operated machines, will be required to produce
thousands of holes in card in each reasonably sized book and it needs
to be hard so it does not constantly need sharpening!"

If you use a punch based on cylindrical rod, sharpening the punch is
a simple matter.  You just grind off a little of the face.  I have used
a diamond hone simply placed cutting side up over the die.  I apply a
little oil, then bring the punch down with foot pressure and move the
hone back and forth by hand.  If it ever becomes too short, you simply
cut and harden another one, or have a dozen made initially.

It is wear in the die which is more problematic, since a good deal
of metal must be removed to remove rounded corners of the hole.
Replacement is the answer.  I used a straight ream for the main portion
of the hole, and a tapered ream to make the hole larger at the bottom
than the top.  I have gone through a number of die holes, but they were
easy to make in modest quantity.

Oil hardening strip steel is also readily available, and easily shaped
and hardened.

Wallace Venable