Two options there that I've used with his stuff:
Free, Librivox.org. Kind of boring and robotic, but loads of Chesterton audio books there. YMMV in terms of quality, as Librivox is read by volunteers, but there's one pretty good one who has done lots of the essay collections.
Slightly more expensive, Theater of the Word. Kevin O'Brian is an excellent Thespian, and a member of the American Chesterton Society, and his theater company has done both the Philosophy and the Father Brown Mystery series in audio books, as well as selected scenes. The debate video I posted was one of theirs, and for just plain Chestertonian-commentary-on-Modern-American-Philosophy, you can't beat the original videos of Stanford Nutting and his rather theologically diverse family (almost as diverse as the non-denominational Guitar Mass Catholic Stanford himself).