I bought a complete 9mm upper half over at the CZ site a few years ago, been watching for a .40 upper half ever since. Got the Kadet upper too, and that runs great on several frames. Only really looks right on a full size frame, even though it works on the compacts too.
Ya just uncommon.
Got to disagree on the EAA, its CZ based and a decent gun but the current large frame production lacks some of the ergonomic refinement of the CZ. For larger hands you are probably ok but for those of us with small paws the CZ is a better fit. Alos the machining is a long way away.
That said, I do have both and like my witness and being able to switch it from 10mm to 9mm to 38 super longslide is sure useful. At some point I may get a .45 upper for it but its a pretty low priority. The kits may require some very minor fitting to function right. My 9mm went on perfect, my .38 super was too tight.