Something else has just come into my mind (always dangerous!).
The company I work for does precision industrial screen printing. It would be possible to print an opaque layer of ink onto an optically clear material such as glass or polyester with a small opening. This would effectively make a pinhole in an 8 micron thick material (cured ink) bonded to a clear support. I might even get round to trying it one day!
This is how zone plates and photon sieves are made.