Don’t worry about finding a case. Just raise the idea of a single cracked tile that needs to be replaced inside a unit … but the tiles are no longer produced. Would anyone put up with a single mismatched tile or would they agree that all the tiles should be replaced in that case?
As previously indicated, once you file for mediation, they may realise you are serious and back right down. When you compare the time, effort and (if they engage a lawyer) cost to the OC, they might realise that simply paying to have them replaced will be the cheaper option.
I know it’s a big step, but you are in the right here and just need to DO IT.