Man, I was in the exact same spot last week wanting to revisit the start of everything. Honestly, just sign up for Audible's free trial—you get a credit to download any full audiobook, including the first 'Harry Potter' narrated by Jim Dale. That's the cleanest, legal way to get the first chapter for free. I did that, listened to 'The Boy Who Lived', and kept the trial because the narration is so good. Some people cancel right after, but I ended up subscribing.
Public libraries are another solid route, though the wait times on Libby or OverDrive can be brutal for popular series. I’ve had 'Sorcerer's Stone' on hold for three weeks now. Spotify also has a weirdly specific selection—last I checked, you could stream the first chapter of the Stephen Fry version if you have any Spotify plan, even the free one with ads. It's buried in their 'Audiobooks' section, not with the music. Avoid those sketchy YouTube uploads that get taken down every other day; the audio quality is awful and it just feels wrong not supporting the official release somehow.