You can purchase rights through specialized marketplaces or by dealing directly with owners:

Buying music copyright typically refers to acquiring the legal ownership of a song's rights to collect royalties or control its use. This can range from purchasing "shares" in a hit song's future earnings to buying out an entire catalog.

This covers the melody and lyrics. It is usually owned by the songwriter or a music publisher.

Platforms like Royalty Exchange and SongVest function like auctions where you can bid on various rights.