This report (17 page PDF) overviews the availability of open educational resources (OER) for business. It surveys a fairly wide range of sources, 24 in all, finds a smallish set of results (169 openly-licensed textbooks, and 76 other resources, mostly aimed at introductory courses), and recommends a set of 16 textbooks that would get a person started on an education in business. The authors note, "a key finding of this environmental scan project isthe need for access to high-quality ancillary learning materials."
If we look at this report - and, for that matter, scan through the results offered by either federated search engines, such as The Mason OER Metafinder (MOM), or aggregation-based search engines, such as OASIS - you encounter what I think is the key weakness of the OER ecosystem, and that is that it is focused on institutional repositories, and thus overlooks the huge body of content (including everything I've ever done) outside the domain of these repositories. How do we create equity not only of access but also of voice when the only resources we count are those contributed by already-established authors and institutions.