The best material I've found for home-made pinholes is the disposable aluminum lids for steam table trays. Here is a link mainly to show what I'm talking about.
http://www.package4less.com/aluminum...isposable.aspx
The lids are less than $1.00 each at retail stores like Party City. You can probably make 50 or 100 pinhole apertures out of one. They are thin aluminum, thinner than a pop can but thicker than aluminum foil. I've found brass shim stock to be harder to work with than aluminum; it can crumple too easily.