I think it concerning that you say they are going to the box and trying to pee but nothing comes out but later on it does in an inappropriate place. To me that says that they know they should be using the box...
I would try the Cat Attract litter, or get the exact same litter the breeder is using. If the breeder is close, then that litter should be easily sourced for you.
I would also be asking the vet about other causes. What tests were done? I see you mention a culture...but what other testing?
You may do better confining to a bathroom for the moment... giving less room for them to miss the litterbox at least. And then observe their behavior from there.
Just do NOT assume that this is a breed issue because you've read of one other instance of a urinary problem! This is a CAT issue not a breed specific issue... now it might be a congenital issue where the kitten was born with something funky in its "plumbing", those things can happen randomly in any cat. But if the other kitten was fine and then started doing this, I might be more inclined to suspect infection. Or a problem with the litter you are using...
I would try the Cat Attract litter, or get the exact same litter the breeder is using. If the breeder is close, then that litter should be easily sourced for you.
I would also be asking the vet about other causes. What tests were done? I see you mention a culture...but what other testing?
You may do better confining to a bathroom for the moment... giving less room for them to miss the litterbox at least. And then observe their behavior from there.
Just do NOT assume that this is a breed issue because you've read of one other instance of a urinary problem! This is a CAT issue not a breed specific issue... now it might be a congenital issue where the kitten was born with something funky in its "plumbing", those things can happen randomly in any cat. But if the other kitten was fine and then started doing this, I might be more inclined to suspect infection. Or a problem with the litter you are using...