Both Westlaw and LexisPlus offer full-text articles from hundreds of law reviews and journals with coverage beginning in the early 1980s. For earlier works, HeinOnline offers a catalog of hundreds of law review articles dating back to a publication's inception. Additionally, many publications offer their articles free online. A good place to find such articles is Google Scholar. 

Researchers can follow this search on HeinOnline to get started, then narrow with relevant key words. 

There are several law reviews and journals devoted to labor and employment law. Select journals and relevant articles for the topic of labor unions include: 

Berkeley Journal of Employment & Labor Law

Catherine L. Fisk, Union Lawyers and Employment Law, 23 Berkeley J. Emp. & Lab. L. 57 (2002)

Richard N. Block, et al., Some Are More Equal Than Others: The Relative Status of Employers, Unions and Employees in the Law of Union Organizing, 10 Berkeley J. Emp. & Lab. L. 220 (1988)

Hofstra Labor & Employment Law Journal

Charles B. Craver, The Labor Movement Needs A Twenty-First Century Committee for Industrial Organization, 23 Hofstra Lab. & Emp. L.J. 69 (2005)

Charles B. Craver, The National Labor Relations Act at 75: In Need of A Heart Transplant, 27 Hofstra Lab. & Emp. L.J. 311 (2010)