The websites of professional associations provide a picture of the profession and often include job postings. If you know the name of an association a Google search will usually turn up their site.
To identify associations, use The Encyclopedia of Associations (Ready Ref. HS17 .G3) or the Gateway to Associations.
Here are some to check out:
American Journalism Review: Journalism Organizations
American Library Association
American Society of Journalists and Authors
Modern Language Association
National Association of Science Writers
National Council of Teachers of English
National Writers Union
Poets and Writers
Teachers of English to Speakers of Other Languages