I am arriving in Shanghai on 12th Dec and then travelling to Beijing on 17th Dec. I would like to buy T104 train tickets (SHG-BEIJING) Is it still possible to buy the tickets on the 12th when I arrive in Shanghai or would it be all sold out by then. Winter would be a slow season wouldn't it? I can speak some Mandarin so buying the tickets from Shanghai train station should not be a problem for me.

thank you
Rachael