Jimbo3,
Here's a source for mylar tape:
http://www.mccormicksnet.com/mccormicks/tapes.htmScroll down to the bottom of the page and look for "Mylar Streamers". The 1/2" wide size used by Teres/Redpoint/Galibier owners costs <$5 for a 100' roll and it comes in colors! Make sure your motor pulley is wide enough before you choose a size.
For cutting the ends and getting them square I bought a VCR tape splicer. It's never been out of the box. I found I can do an excellent job with a new #11 Xacto blade, a straightedge and a clean, flat working surface. It helps to be nearsighted, and no caffeine!
Some people use VCR splicing tabs but I've had better results with 1 mil x 2" clear 3M shipping tape. My splicing tabs always seemed to separate after awhile. My shipping taped belt is as good as the day I made it, seven or eight months ago.
If 1/2" black mylar will suit, I'll gladly make a belt up and ship it to you. Let me know the length you want if you're interested. Like Cello, my 100' roll should be enough for several lifetimes.