One of the issues this year has been the lack of Democratic debates, as well as the ability to easily find them online after they happened. It took a bit of searching but below I have the videos for all of the ones that have happened so far. I also have all of the other forums, debates, etc., where the democratic candidates have attended that I was able to locate. They are ordered by the most recent first.
Feb 11, 2016 6th Democratic Debate on PBS:
Feb 4, 2016 5th Democratic Debate:
Jan 17, 2016 4th Democratic Presidential Debate:
Dec 22, 2015 3rd Democratic Debate:
November 14, 2015 2nd Democratic Presidential Debate on Vimeo:
October 14, 2015 First Democratic Debate:
Below are other forums and debates where the democratic candidates participated:
February 19 MSNBC Town Hall Part 1:
February 19 MSNBC Town Hall Part 2:
January 11, 2016 Brown And Black Democratic Presidential Forum:
November 21, 2015 Presidential Justice Forum hosted by 20/20 Club and BET:
November 6, 2015 MSNBC Democratic Presidential Candidates Forum On Vimeo:
Let me know if I missed one.