This kind of question is best asked when you’re logged in or by email, because then we can answer privately, rather than publishing it to the blog. (I don’t mind answering non-WAYWB questions, but I don’t want to clutter people’s dashes with unrelated asks).
It’s available on iTunes UK and Audible. It was previously on YouTube but appears to have been taken down (guessing it was prompted by the BBC, as John Finnemore has said he doesn’t mind people listening to it that way). As far as less legitimate ways of listening, I have no idea. I bought them from iTunes and haven’t looked anywhere else.
Other anon: Just an FYI, the tumblr user icarusing has a high-quality cabin pressure masterpost.