Chad has it right, it's Italian poplar bender board. I knew I was on the right track when I found a lazer cut piece in a kit that was marked "Made in Italy". I get 4x8 sheets from a company called MacBeaths Hardwoods. They have locations in Utah, California, and I think Arizona. Runs about $20 per sheet. You might try calling around to high end cabinet makers in your area. Any shop doing radius work in cabinetry will have scraps and know where to get this stuff.