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.
https://www.surfasonline.com
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?
http://www.at-la.com/cities/santa_fe...ial.htm#plasti