Where did they get the DVDs of a movie that just got released?
Both are very good questions. Nobody in NK would likely have a DVD player and I doubt this will be on DVD for a awhile.
That’s easy. You get a good, quality video camera and take it into the movie theater, record the movie while it’s playing, put it on a DVD, and send it up on a balloon.
Movie leaks happen.
A LOT.
There are a lot of people involved in the duplication & distribution process, and it’s not unusual for someone to make a copy. At some point it’s just a big file on a computer’s storage device, and at worst it’s just a matter of copying a 200GB file. Consequences may be severe, but leaks do happen; reasonable speculation includes it happening with guarded permission.