If you don't want to use a source of questionable legality like Sci-Hub [1] then you can try sending a request to the authors to make use of their right to share a copy through the Open Access Button [2] or Unpaywall [3].

[1] https://en.wikipedia.org/wiki/Sci-Hub

[2] https://openaccessbutton.org/request/zsLh3M7ozGvLwD67v

[3] http://unpaywall.org/