It's questionable to look for things like forum posts. If at all possible, regular publications are best for things like this, and if not those, then static websites. A "forum post" is basically a personal testimony that could have not even come from a person -- not a good source.
Search for newspaper publications about tournaments (Things like TBH usually got mentions in local papers).
The eSports ePapers are good too (daily dot esports, etc.)
Try to set-up a skype interview with a famous & storied smasher, use that as a primary source and get their word as a veteran professional about how the game has grown.
At the risk of almost doing your paper for you...Here's a framework I would personally use off the top of my head:
Source 1: Documentary
Source 2: Local newspaper article about local "big" tournament, exemplifying that it used to be a sporadic/local thing
Source 3: (Primary Source) Skype Interview with professional veteran
Source 4: eSports news about smashers being sponsored by famous eSports organizations like TSM, exemplifying we esports now
Source 5: Sakurai or Nintendo action against EVO or community in general to show the struggle
Source 6: eSports news/article that generally speaks about Smash and its history/progression
Source 7: How Nintendo got into EVO by raising money for cancer research and/or how Smash The Record does so much for charity
Source 8: meleeitonme is a great source of information ofc.
Source 9: Primary research using smashboards tournament rankings to show how tournaments are insanely widespread and have grown over the years (
http://smashboards.com/rankings/melee/league/events?sort=value&order=DESC)
Source 10: Mew2King's clashtournaments-published list of frame data and etc. can be used as a source to exemplify how obsessed this game makes people.
Good luck with your paper, make it worth reading.