How early should I buy a Beijing-Lhasa train ticket?

I'm in Hong Kong and I want to take the train from Beijing to Tibet at the end of June. All the travel agencies here say I must go to China to buy the Beijing-Lhasa Train ticket. They have also said I can only buy the ticket 3-4 days before departure date.

Is this true? How much in advanced should I buy the tickets? Will they sell out?

Also can you reccomend a good travel agent who can arrange the ticket and the TTP?

Thank you!
-Lisbeth

you can try the travel agent in hong kong - china travel, the most reliable agent, you need to check with them directly
http://www.ctshk.com/english/aboutus/local.htm#01<BR><BR>or you can visit the following website
http://www.tibet-tour.com/<BR><BR>in china they will not sell out the ticket once you get money

I tried China Travel they couldn't do it.

So if i buy it in beijing how many days in advanced must I buy it?

They don't go on sale any more than 10/11 days before departure date anyway.
Cheers!

It's true that in China you can't buy tickets too in advance.