From Kunming International Airport, where to get bus to Ya'an? And how long would it take?

For Ya'an, do you refer to the one in Sichuan Province?
If so, there is no direct bus to reach Ya'an from KM airport.
It is suggested to fly to Chengdu first. Then take the airport shuttle bus 303 to reach Minshan Hotel. Then you can take a taxi to reach Xinnanmen Bus Station, where you can find the direct bus for Ya'an.
The bus from Chengdu to Ya'an takes about two hours to two hours and a half. The flight from KM to Chengdu takes about 40 minutes.