I bought a large irregular piece of 2" thick cutting board scrap from Surfas Restaurant Supply in Culver City, enough to make a couple of boards for contests. I think I paid $5 for something they couldn't otherwise sell.
Call over to their fabrication shop and see if they have anything that will work for you.
With all the industrial business along the 710 / 5 corridor, there's gotta be a local source for new material. Maybe give a call to the plastics companies here?