Is Yak Cheese available to buy in Kunming?
There are a few Tibetan restaurants that might sell you some, never tried myself though.
You can search Tibetan in the listings.
Otherwise the best I recommend for sure is Geza Gold, produced by a Yak Cheese NGO sort of co-op in Shangri-La.
It's available all over the old town up there, but I believe Flying Tigers Cafe also now sells products including the cheese on their website and will ship within China.
In Kunming ordering from them is probably your best bet.
My wife ordered yak butter on Taobao. She did not realize it is supposed to be rancid.
I bought Yak Cheese from an eco- agriculture products shop run by a social enterprise in Yunnanyinxiang 云南印象 Beishiqu 北市区. The quality is better than what I found in markets.
Here is a good blog article about European-style Yak Cheese