I've been waiting for the more experienced members to answer your question, but since no one else has responded, here is my $.02.
I checked the CZUSA website and they don't list the 40 or 9mm slide and barrel as available parts. I suspect that you could special order them from CZ USA, but that is only a guess.
I think than overall, it would be more expensive to try to get the capability you want this way than to go the usual route of buying a complete 9 or 40 gun and then adding the Kadet kit. Obviously, the supply line is set up to treat the kadet as the add on option, not the other way around.
I also have a Sig 9mm in addition to my CZ's and find I get different enjoyment out of shooting each gun. If I were you, I'd get the CZ of my choice and then add the Kadet....Wait, that's what I just did!!! Best