http://www.amazon.com/Turntable-Toys-TC-1-Audiophile-4-inch/dp/B00JD38XDQ/ref=sr_1_1?s=electronics&ie=UTF8&qid=1463081600&sr=1-1&keywords=turntable+toys+mat
You can make them easily with cork from Home Depot too. I'd love to support UTurn but that's quite a ripoff.
Mine is warped too as is my friends. Pretty sure the warping was the reason for the steep steep discount. And my packaging was weird but not likely the cause of the warp.
It plays fine though. Someday I'll by a flattener. Someday.