The artificial star LED torch from Hubble Optics in HK has a front plate with apertures from 50 micron to 250 micron.
http://www.hubble-optics.com/artificial-stars.html
I've "converted" mine to fit the trusty ol foucault tester so that I can have "test" stars using the flouro lamp for the spectroscopes....
Another idea... this diaphragm might be usable as a "aperture stop" for photometric or spectroscope applications...