I made my own for my kit and they're holding up and working great!
i followed this guide
http://www.edrums.info/5.htmi used pet screen found at lowes but im sure there has to be an equivalent at a local hardware store or home improvement store.
lots of people use the sunscreen? or solar screen for the top layer because its a little tougher, im still not even sure where to purchase this though.
much cheaper than buying them and for 8" or 10" heads it wouldn't take very long at all to make them. just remember to cover them with another layer of screen (not attached to the rim) and they should last for a while.
but mine are for my a to e conversion im not sure if the same set up would fit the pads, but you could always forget the extra layer and buy a patch, this would match the billy blast look you're going for.