Chipboard (a.k.a. cardstock, patternboard, etc.) can be purchased at a local paper supplier. Most sell 26 point chipboard by the bundle (approx. 80 to 100 sheets) for about $54. Check sheets 26" x 38" which is a nice, large piece to work with. Purchasing in bulk saves a few cents per sheet and ordering from a qualified source (like these or another paper store in your area) assures that you will receive good quality chipboard.
Sample:
MILLCRAFT PAPER STORE Locations:
http://www.millcraft.com/locations.html
ULINE:
http://www.uline.com/BL_1852/Chipboa...FQyFQAodu1Jmrw
National Packaging:
http://www.nationalpack.com/PAPER-PR...D/c-1-155-174/
Are just a few.
Jim