I always thought flash was just a laminated piece of paper that you can buy anywhere.
http://newyorktattoo.com/thermal_ima..._279_prd1.htmi found that, but i dont know if it is a certain type of paper you use for flash. Im guessing the only other materials you would need are your imagination , a theme , markers or colored pencils and the flash should all be apart of one theme. If your doing tribal, all of the flash for that paper should have tribal. Thats just my guess, i have never really done much research on flash itself.