Have you tried contacting IMG in Taiwan?
…is the main site, but try to find your local Taiwan agent. That’s the best lead that my wife has found so far, at least in my case. My current dilemma is the same but different 
. I need insurance to cover a four month lapse until I’m eligible for national insurance here. Anyway… Not to answer a question with a question, but I’ve been looking at various plans and trying to get info, so I’ll share with you some links that I’ve uncovered.
You mentioned “various UK plans”. Did you try BUPA?
What put me off of them was the fact that I’d need to sign up and pay for a year.
Ironman sent me the following link in response to my post a while back:
[forumosa.com/taiwan/viewtopic.ph … ate#171324](Int'l Health insurance for Taiwan expats not covered by NHI
There’s some stuff in this thread that might help, meanwhile
I’m still looking for a solution to my problem and will follow the progress of your thread.
Hope this helps.
-P