www.hainanairlines.com is in English--and won't admit the flight I want exists (found via Google Flights).
www.hkair.com is in Chinese, has no problem with the flight but it's all in Chinese and there's a captcha that's stumping my wife.
Their phone number doesn't seem able to book a ticket.
So far my e-mail to the support address I was given has produced nothing but an autoresponder.

There is a domestic leg on Alaska. Last time we did this we booked with Hainan and their baggage rules applied but it looks to me if I book anywhere else Alaska's rules would apply on the outbound.