I'm lucky I have a specialty store near me (Seattle Fabrics) that sells strips of reflective tape, reflectorized grosgrain ribbon, even reflective-coated ripstop nylon. I add this stuff to EVERYTHING. But Denise is right - active lighting is way better than passive systems ilike textiles and reflectors. Reflectors only work at very limited angles, and things like coated fabrics have that same limitation as well as not working when they're wet! Sheldon Brown has some really interesting articles on reflectors:

http://sheldonbrown.com/reflectors.html