Here are a couple places to purchase the plastic canvas:
Plastic canvas (.79 to $1.89) available at:
http://www.everythingplasticcanvas.c...-mrl-c260.aspx
Create for Less has it from .59 per sheet, but must be bought in multiples of 12 sheets, at:
http://www.createforless.com/search/...astic%20canvas
Yarn tree has some, but pricey:
http://yarntree.com/cross-stitch/ind...646c818bdfdc80