Look primarily for what you will want used for the focus of the final product. The interior pages or text sheets will come more naturally based on your first choice. Some handmade papers are too thin, will not run through a printer, do not fold well, etc... I will let you know.
To make the search easier, I keep inventory & sample books of handmade papers in my studio as well as my own line of handmade papers.
Art Paper - http://www.artpaper.com
Eco Paper - http://www.ecopaper.com
Just Paper - http://www.justpaper.com
Handmade Papers - http://www.handmadepapers.biz
CABA Paper - http://www.handmadepapers.com
Japanese Paper Place - http://www.japanesepaperplace.com
Daniel Smith - http://www.danielsmith.com
Handmade Papers - http://www.handmade-paper.us
Dick Blick - http://www.dickblick.com
Hallander's - http://www.hollanders.com
Flax - http://www.flaxart.com
Eco Saviours - http://www.eco-saviours.com
Paper Zone - http://www.paperzone.com
Marco Paper - http://www.marcopaper.com
University Products - http://www.universityproducts.com
Paper Connection - http://www.paperconnection.com
Eco Africa - http://ecoafrica-usa.net
Handmade Paper Online - http://www.handmadepaperonline.com
Phenix art Supply - http://phoenixartsupply.com
Paper - http://www.paper.com
Crafta - http://store.crafta.com/decorative-paper.html
Plain Paper - http://www.mlcltd.com/plainpaper/
Paper Works - http://www.paperworks.biz
Paper Origins - http://www.paperorigins.com
Sakar - http://www.sakar-handmadepaper.com
Paper Mojo - http://www.papermojo.com
Talas - http://www.talasonline.com
February Paper - http://www.febpaper.com
Savoir Faire - http://www.savoirfaire.com
Potpourri - http://www.potpourrionline.com
University Book Store - 4326 University Way NE - handmade paper not shown on .com
Seattle Art Supply - 2108 Western Ave - handmade paper not shown on .com