It looks like Forkyz (in its current version) reads more than just PUZ files now:
Support new input formats (AM Universal JSON, Exolve, PA Puzzles HTML, Spoonbill, Wall Street Journal JSON, .xd, XWord).
[This page] (https://github.com/doshea/nyt_crosswords) is linked from the Forkyz list of sources page you linked. It was the first one I clicked on, and it is a huge archive of JSON files.
I’m very sorry to hear about your dad, and I hope this can help in some way.
