Thanks for the info! Lidl (US) just made their Grill Meister Kamado-style Ceramic Grill available in the USA and I snagged one. I'm researching, and trying to figure out how to make a heat diffuser before I even open the box.
Unfortunately, I already bought a bunch of terra cotta saucers from Amazon, and it's too late to cancel delivery; hopefully I can return them. I was planning to sit them inside a 7" pie plate, which I would somehow jerry rig to sit above the coals, so cracking probably would not have been an issue. (I could still use the plate with sand, or perhaps the ceramic beads one uses for pie weights?)
In any case, after extensive searching, I came across a site that has discontinued 8.5" pizza stones for sale. It may be too big to work as a heat diffuser for my particular grill, but I think it's still a good find and might work for those with slightly larger mini kamados. (Or one could just use them as intended, as personal pizza stones.)
FSX Market -8.5" round Cordierite pizza stone In addition, they have a coupon code for Memorial Day 2021: FSXSAVE15
Technically, Pizzacraft.com also offers small, 8" stones, but they're entirely out of stock of any pizza stones at the moment.
I am not in any way affiliated with any of the aforementioned brands or companies. I just appreciate the help offered on this forum and wanted to contribute.