Battery out of stock - more coming?

You do know that the Chinese company Huawei makes the Nexus 6P, right?

There's no such thing as a non-Chinese battery.

I would check Aliexpress and Amazon.com for a decent replacement battery. The higher the rating the better the quality, but be sure to actually read the content of the reviews. There are some sellers (even on Amazon) that buy fake reviews.

OEM batteries are long gone (confirmed over a year ago when I called Huewei tech support). Most batteries on the market are poor imitations of stock and to this date I have not seen any examples that include the temperature sensor needed to enable the rapid charging feature.