I have a constant supply of target material through my job. I work in the graphics printing industry and we go through thousands of sq ft of pressure sensitive vinyl daily. The digitally printed vinyl needs to have an overlaminate applied to it, so the backing material from the overlaminate is separated and wound onto a separate core, That backing material makes a great media for patterning. It's typically 48', 54' or 60' wide by 150' long and ends up in the recycling or trash dumpsters. I'm sure if anyone has a graphics printshop nearby that does digital printing, you could get yourself a free supply of target material if you request it.