American Association of Law Libraries
Australian Law Libraries Group
Bates Information Services
British and Irish Association of Law Libraries 
Find out more about volunteering for the British and Irish Association of Law Librarians:
https://www.youtube.com/watch?v=Kw5CixdZL9Q&feature=youtu.be
Canadian Association of Law Libraries
International Association of Law Libraries
International Federation of Library Associations
New Zealand Law Libraries Group
Special Library Association, Legal Division (USA)
UNESCO Libraries Portal

For a much more detailed list,

The International Association of Law Libraries (IALL) and

Lyonette Louis-Jacques’

Other Law Library-Related Associations and
International Conferences on Legal Information and Law Librarianship