Ah, they're delightful books, and I picked up the full set during the Kobo 90% coupon days.
. The first one is a bit weak, but they start picking up after that.
ETA: Unfortunately, there are only three of them that are available in unabridged versions at Audible.com, all read by the superb Frederick Davidson (real name, David Case). AudibleUK has a full set, but read by Samuel West, an unknown quantity to me, and these also appear to be the ones at Audible.ca, though I don't have an account there.