You could try Sci-Hub and LibGen. If you don't find what you're looking for, you can always email the authors or other scholars who may have access to the paper you're interested in.
A less alternative site would be arXiv, but it just has preprints.
Emailing the author has quite a good succes rate. Many just forced to use a publisher to get it out but love giving their paper to those who are interested.
Atleast that's my experience in trying to get certain papers for my studies.