Well, Audiobooks' genre is very reserved and not much participated by community; that's why there are few place to look for Audiobooks. No Scene group(s) release Audiobooks (at least in English) and
MAM is only countable place for Audiobooks. Though I won't recommend biB as nothings there in terms of Audiobooks, Usually
MAM stuff. But AudiobookTorrent (
ABT) may help but they are under-maintenance so when they'll be back check them. Otherwise use
TPB, Demenoid, KAT etc for Audiobooks apart of
MAM.