Try checking here!
http://www.zennioptical.com/
I've never personally used them but I've heard good things and have been thinking about getting some for Anita Radcliffe from 101 Dalmatians and a pair for my gf for a Homura cosplay because she needs glasses in real life and we don't want her walking around with eyestrain all day xD;;
It seems really convenient because if you need a prescription, you can get it, or just get plain glass.