@pillface I have also had a couple of emails back and for MetService. In February 2020 Brad from the MetService told me they realised the data they made public was lacking in comparison to other weather services around the world. They are updating their API to make more data available. It was supposed to take at most 18 months, which would mean it should be coming online now at the latest. Their exact quote was:
"However, we are making further changes to increase accessibility and reusability of observational weather data. For example we are developing an API that will make a wider range of data publicly available, specifically aimed at supporting the development of innovative weather products which should be available later in 2020. The new www.metservice.com will enable us to provide users with access to value-added data sets, including additional observational data. We intend to implement this capability in the future - likely in the coming 18 months."
It might be worth trying to email them again if you have time. I tried a few months ago but didn't hear anything back this time. So maybe I've worn out my welcome. :)