Since there are so many different Dialytan 4x models by various manufacturers which also differ over the periods it is impossible to answer your question. Generally I've not seen "spare lense sets" for sale, best would be if you keep your eyes open for another donor scope to kill for parts.
I had one scope sent to Don Miller for repair and he had replacement lenses available to put in due to a crack. You could send to him for repair. His email:
I had one scope sent to Don Miller for repair and he had replacement lenses available to put in due to a crack. You could send to him for repair. His email: