Corrugated fiberboard sources:
Your local appliance dealer has refrigerator and dishwasher size cartons for free. Cut them into any size you want, just make sure that the corrugations run parallel to your airflow so the moisture can be easily blown out of the stack. It's usually a heavier grade of paper, so they'll last a loooong time. Don't worry about water resistant board, you'll remove all standing water off of the print before putting them into your drier anyway.

Ask any dressmaker about interfacing, and they'll use the phrase "Pellon". Read about it here:
http://www.pellonideas.com/content/view/14/30/

For non-woven materials, DuPont's "Tyvek" is very good. Read about it here:
http://en.wikipedia.org/wiki/Tyvek
It's available in thicker 18lb sheets (thicker = better), 25 sheets, 17 x 22", $38.99 here:
http://www.allweatherblueprints.com/...-18172225.html

Another non-woven olefin product is "Reemay".
Gaylord promotes it as "an interleaving material when drying wet photographs" here:
http://www.gaylordmart.com/adblock.a...8611A8DA39F707

Personally. I find acid free blotters work very well in my homemade drier discussed here:
http://www.classicbwphoto.com/Blog/A...A95E8D0C0.html

Conservation grade blotter papers are also from Gaylord here:
http://www.gaylordmart.com/listing.asp?H=3&PCI=128007

If you want to go First Cabin, you can get archival corrugated board from Gaylord here:
http://www.gaylordmart.com/listing.asp?H=3&PCI=128003

That oughta get you started.
Have fun.

Reinhold