One route that's sometimes overlooked is public library apps, especially if you're in a region with strong digital lending. Apps like Libby or OverDrive work with your local library card to offer a vast catalog, and yes, that includes all the Harry Potter audiobooks, both the Jim Dale and Stephen Fry narrations. You 'borrow' them digitally just like a physical book, download for offline listening, and they return automatically.
It's a completely legal, free option, though availability depends on your library's collection and there can be waitlists for popular titles. I had to wait three weeks for 'The Half-Blood Prince' last summer. Still, it's a fantastic resource if you're patient. The app interface is decent, and it feels good knowing you're accessing it through official channels.
Your other main option is purchasing through retailers like Audible, Apple Books, or Google Play. This gives you permanent ownership and instant access, obviously, but it's not free. Audible's subscription model includes a credit each month which can be used for any title, so you could effectively get it as part of your monthly fee. Just be aware that after cancelling a subscription, you keep the books you purchased with credits.