Is train ticket still available fr Kun Min to GuongZhou between July and August,where to buy?

Yes, the train ticket still available from Kun Ming to Guangzhou between July and August. You can buy it at the train station or the ticket outlets in Kunming. Or you can book it online through some agent in advance. Here is an agent's ticket booking website for you: https://www.travelchinaguide.com/china-trains/ .