If you wanna selfhost your own solution, I can recommend Audiobookshelf. It scraps metadata from Apple, Amazon, Google etc, tracks on a per-user basis at what point in the book you are, can be used in a browser and has an android app. It’s easy to set up with Docker too. You can even add PDFs and epubs to the books.
Been using it for a few months and it has been great.
As for sourcing of audiobooks, aside from torrents there are also audiobb.com & audiobooksbee.com . They use RapidGator as host for a ddl.
…yet