Hello all, I have been following this most interesting thread.
As a retired magnetics designer and manufacturer, virtually all commercial firms are fabricating mass production in China. The set-up is costly and runs of less than 1000 difficult to get a quote. Your experience with Sun is typical.
Some HV transformers need special core shapes, custom bobbins, litz or very fine guage wire and/or a special winding machine. So not easy to design, tool or build.
Finally the impregnated secondaires needed a vacuum oven to pull air bubbles out of the epoxy, plastic or varnish liquid before it cures solid. Any voids or air bubbles remaining will eventually ionize and lead to carbon tracking and failures.
In mid 1980s it took us 1 yr to design and to debug the potting process and materials for a 12 kV custom avionics CRT module with transformer and voltage multiplier! We made 1000s but always got some DOA after potting, yields increased from 50% to 98% after the procedure was optimized.
Just the rumblings of an old retired EE!
Jon in Paris