Visa China Transmongolian Express

Goodmorning,

I am a traveler from The Netherlands and I am considering taking the Transmongolian Express from Beijing to Moskou. If I want to do so, I will need a Chinese visa. I am currently in Sri Lanka and I was wondering if it is possible to arrange the Chinese entry permit in Colombo. If yes, what are the costs? And what are the requirements?

Thank you in advance. 
Kind regards, 
Anne Harteman