Kunming to Yuanyang long distance bus ticket- can I buy in advance in Shanghai?

Hi,

I'm hoping to travel from Kunming to Yuanyang (to see the rice terraces) on 15/02. I arrive in Kunming on the 13th, however I'd rather not wait until then to go to the bus station in Kunming as I'm worried the tickets may have sold out by then.

I'm currently in SH, so my question is, is there somewhere I can go in SH to purchase these tickets (one of the large long distance bus stations/an agency somewhere) in advance of travelling to Kunming or do I simply have to wait until I get to Kunming, go straight to the bus station and hope for the best?!

Any help or advice here would be greatly appreciated.

Cheers,
Jason