I, too, want this blech. In addition to its halachic advantage (which may or may not change the way you can use it), this blech supposedly provides a lot more surface area and is good at keeping food warm at the right temperature without burning it.
Another name for the unblech is the "water blech" or "k'deirah blech." You may have better luck searching for these. Meanwhile, here is the source I have found. From here:
I have a K'deirah ("the unblech") and I love using it because it can
keep food nice and warm! Try contacting K'deirah Corporation, [...] 8818 N. Kolmar, Skokie 60076, (847)673-3210, and [a representative] will be
able to tell you where you can get it. Feel free to tell her I sent
IY"H I will call her soon but if you beat me to it, please post what you learn about where to get this.