I don't know how well this stuff works yet, but Jandd sells some reflective tape (adhesive or sew on). I noticed it when I was ordering a saddle bag and added it to my shipment. It's $1.50 for a 12 inch strip. I have seen reflective stickers at bike shops for like $6 so it seems a reasonable price. They don't overcharge for shipping either.
Here's the link:
http://www.jandd.com/detail.asp?PRODUCT_ID=FREF