[Bruce MacCulloch]

Actually, Beorn is mentioned in Lord of the Rings. His descendants are spoken of by Gloin as still guarding the Carrock.
As to the number of Maiar, there are certainly more than just nine. The Silmarillion and other books make constant reference to them, with terms such as "the folk of {insert Vala here}" and also by naming them. Besides, there are more than nine Maia that are named, much less mentioned. {i.e., Ilmare, Eonwe, Osse, Uinen, Melian, Sauron, Olorin (Gandalf), Curumo (Saruman), Aiwendil (Radagast), Alatar, Pallando, Gothmog, and the rest of the Balrogs (be it 3,7 or thousands); and these are just some of the ones specifically mentioned}