If you are looking for specific versions of movies (like an original theatrical mix that isn't on the DVD), fan-edit communities often host separate audio files. 🛠️ How to Add the Audio to Your Movie
Russian trackers seem counter-intuitive for English audio, but is a goldmine. Russian users often remux Western Blu-rays and include the untouched English DTS track as a separate downloadable file. Where To Download English Audio Track For Movies