Thanks for the suggestion to try InsureWith. Did the online application, and was declined cover. Not really suprised, but it was worth a go.
Regardless, I'm hoofing it back to the USA for a road trip around the SW states (like you see in the movies) and hopefully returning early December via Hong Kong (with all its COVID compliance). A bit reckless? Who knows, but I'm at that point now where I feel this may be my last opportunity to do such things, and I'm not prepared to give up on these dreams just yet, despite all the obstacles like medical insurance, airlines changing flight schedules, lousy exchange rates, and the slight(ish) worry that things could go horribly wrong.
My GP thoroughly approves, and he knows what he's talking about, so that's all good. Wish me luck!