Try Dick Blick art materials - I'm pretty certain I saw scanner board in the
last catalog. They have an 800 number, which I forgot to bring home, but you
may want to surf over to their website - I assume the catalog is on line
there;

          http://www.dickblick.com

I get drafting mylar by Dupont from them, and a lot of other things as well.
Their motto is "Dick Blick ships quick", and I have found it to be true -
usually I get my order in 1 or 2 days. Prices are reasonable on most items
too, and they will sometimes try to find some things that aren't in their
catalog - I've had good luck with them. Customer service good too - I even
got them to agree to discount the price of Hunt #104 nibs if I buy 100 at a
time - and we really go through them doing lithic illustrations (mylar eats
the nibs for lunch), so I don't mind buying 100 at a crack (with the
company's money, of course!). Lots of interesting stuff in the catalog, and
in a wide range of media. Worth checking out, in my opinion.

Liz Hansen
Sketchbook Graphics
and
Sr. Illustrator - Center for American Archeology
Kampsville, IL