go to
http://www.mcmaster.com and look for the part number 86375K144
This is the material that lots of DIY'ers use to make their own cones. In terms of how to make it, look at this thread:
http://www.vdrums.com/forum/showthread.php?t=26778you will need to sign up and join the forum to see the pics. GREAT site for info.
the reason why we have the cone is to have a way to connect the piezo to the mesh head without compromising the piezo's destruction. Basically, it softens the hit to the piezo. There's also some technical reasons I think about the vibration of the mesh head. i dont' quite remember. But you do need some sort of foam between the head and the piezo.
Oh, I forgot. You don't need to make the cones as cones. That is, you can make them into "castles". Look at this thread. Don't forget to join the forum to see the pics.
http://www.vdrums.com/forum/showthread.php?t=37936edit:
another great webpage to take a look at:
http://www.toontrack.com/forum/tm.aspx?m=35473