I was wondering what kind of camera you use and what your focal length is? I recently got me some "perfect pinholes" normally used for elektron microscopes. If I have the right size for you, I'm willing to mail you one so you can experiment with it before buying an "expensive" pinhole? In return you can send me a nice print made with the pinhole.
Send me a PM with your address if interested.
"Have fun and catch that light beam!"
Bert from Holland
my blog: http://thetoadmen.blogspot.nl
Linkedin pinhole group: http://tinyurl.com/pinholegroup