I bought my insul-brite from www.homesew.com . I had a coupon at the time and used it. I had never worked with this type of batting so I thought I'd try it. I still haven't got it though. LOL.
Here are a few other sites that you can also order it from:
http://www.reprodepotfabrics.com/nslbrt.html
http://www.fabricsunlimited.net/inbywaco.html
http://www.homesew.com/SpecialtyFabrics.html