Añadiendo información sobre mi mensaje anterior, he encontrado esto en su propia web:
How many days in advance can I book China train tickets?
China train tickets released 15 days before departure online. At train stations and ticket agencies, tickets also go on sale 15 days in advance.
But you can book tickets with China Highlights more than 30 days ahead. Actually, it is recommended that you book tickets with us as early as possible, especially during Chinese holidays and peak periods.
Obviamente con su comisión