I'm sure those are "home made" backers. Call plastic supply company in your area or try this webpage -
http://www.coroplast.com/distributor/Personally, I don't like coroplast backers because of the way light shines through them. You'll have to use spray tack to hold your targets on. If you use paste, the targets will rip. If it is windy when you are putting on new faces, the adhesive can blow and land on your glasses. That really sucks, because you'll need a solvent to get it off.
