Saregama holds the largest library of old Bengali classics. You can purchase and download individual MP3s on their website. For ZIP files, check their "Album Bundles" section where they offer complete movies or artist-specific compilations.
If you search Google, you will find dozens of blogs with titles like "1000+ Kumar Sanu Songs Free ZIP Download." Here is a checklist: Kumar Sanu Bengali Mp3 Song Zip File Download
While primarily a streaming app, Gaana’s paid tier (Gaana Plus) allows you to download songs offline in MP3 format. You can create a playlist of Kumar Sanu songs and the app will store them on your device (often in a secure format, but some tools allow extraction). Saregama holds the largest library of old Bengali classics
If you are putting together a collection, these are the essential tracks often found in top-rated zip files and albums like the Kumar Sanu All Time Hits : Tumi Achho Eto Kachhe Tai Priyotama Mone Rekho Tomar Sure Sur Bendhechhi Keno Tumi Amake Je Eto Bhalobaso Film Hits: Chokher Bhasa Jodi Jatoi Karo Bahana Duniya O Duniya (composed by R.D. Burman) Devotional & Modern: Mayer Paayer Jaba Hoye Amar Sadh Na Mitilo Where to Download and Listen Legally If you search Google, you will find dozens