I find it baffling that I can't find a converter for Thunderbird to
Outlook .pst format.

There are a series of 'methods' on the mozilla site as to how to do
this but they all involve intermediary software, are labor intensive
and only seem to work a third of the time according to reviews.

I even found a Thunderbird plugin which exports in three or four
different formats but none of them could be imported by me.

Any suggestions?