http://www.photonovelty.com/Choose item number GW1620 and use code SBUG810. Regular price is $32.95.
Shipping to NY came out to $11.29.
They ask for your resale tax ID, but any random string of numbers work.
I haven't seen their quality yet, but they're part of Denny MFG, who make some of the best photography backgrounds and props in the business. Presumably that'll reflect on the quality of their canvases as well.