Reese Supply in Dallas is a wholesale sign supply company that sells the 3M ScotchCal clear vinyl that the clear bra people use. Make sure you get the 3M brand as they have substituted Avery for me one time and it doesn't work as well. They have a city sales door at the back of the building and sell the material by the yard. Usually comes in 15" & 30" rolls at about 5-6 dollars a yard, IIRC there are different thickness by by the top of the line film it not expensive. They take cash, check or credit card. They also sell almost every color imaginable.
Are you putting it on a road or mountain bike.
http://www.reecesupply.com/
Reece Supply Co. of Dallas, Inc.
3308 Royalty Row
Irving, TX 75062
Toll Free: (800) 776-7448
Local: (972) 438-3131
Fax: (972) 721-1758