Silk is tricky to work with if you are not used to it -- very slippery, can snag, etc. It seems like a much better idea to purchase readymade silk pillowcases!
I did find these on Amazon, which are made from charmeuse silk:
http://www.amazon.com/Spasilk-Facial.../dp/B0027IS1O0
Edit: Oh, and I found this website that sells charmeuse 100% silk for about $20/yard:
http://www.moodfabrics.com/fashion-f...charmeuse.html