It’s a somewhat complicated situation without a clear cut answer.
If playing for a public event, you MUST secure rights for playback. Most music is covered by either ASCAP or BMI.
Generally speaking, the venue is the one that secures this. It gets a little more complicated if the venue is temporary or if they do not regularly host events.
Additionally, if it is a private event, you may be able to present an argument against needing to pay the fees.
Regarding gaining access to a music library, that doesn’t seem to have changed much over the years. While the agreement within services such as iTunes may say it can’t be used for commercial purposes, there really is no true avenue available for DJs to get the music.
It would be neat if there was an option, but until there is, you’ll have to get it where you can.