Enro,

There is a thread on this over at CR. They mention Baader filter paper. I just picked some up from http://www.astro-physics.com/. There also seem to be several filters made from the material for telescopes. I found some "astrozap" filters here: http://www.optcorp.com/productList.aspx that seem to be from the same material.

Maybe you have a local photography/telescope store that has some of this material.

Good luck,
Brant