I make my own out of fun foam you can find at the Dollar Tree or in the kids' craft section at your favorite craft store. Dollar Tree foam I think is 1/8" thick. I attach it by using Aleene's Quick Dry Tacky Glue. You can also run it through your Xyron. You can use your ATG gun or double stick tape too.
Scotch also makes excellent foam dimensional. I used to buy my dimensionals in the hardware department.