You don’t need to "download" from shady sites. Just subscribe to legal OTT platforms that host the movie.
The non-profit digital library hosts some old Tamil radio recordings. Search for "T.S. Balaiah - Thiruvilayadal Dialogue Archive" . These are often in public domain or low-quality radio rips. This is the only legitimate direct download method without streaming subscriptions. thiruvilayadal murugan dialogue download