Tzu Chi Foundation (慈济, CiJi) often travel (via hired chartered buses) to rural outskirts 50-150km (or farther) from Kunming to provide supplies & assistance to those in need.
This Kunming-based charity organization may welcome foreign English teachers for their frequent missions. Not sure. You'll have to touch base with the Tzu Chi volunteer leaders (info end of post).
Many of the members are Buddhists, but you don't have to be one to join. Compassion & time, all that are required. Tzu Chi has world-wide reach. Their members consist of retired or active professionals with day jobs who find free time to help the impoverished, the sick, the foster children, or the elders.
For reference, here's an old English article published by their foundation, titled "Tzu Chi Delivers Winter Aid to Thousands Across China - Yunnan:"