John,
Thanks for your suggestions. Unfortunately, these were a dead-end. Metric does not work for me, but I was able to call Steve Chappell Squares directly and he said he could make me a 36 x 24 inch square, but it would be hugely expensive to just make one. The Alibaba supplier is inactive now. And, the Woodpecker tool company no longer makes the 36" square, since they are no longer able to get the materials. Apparently they had trouble with it being too "wavy".
I guess I will just have to go down to the local hardware store and settle for the 24 x 16. Thanks again. I can't believe it's so hard to get something like this!