I just found out the watermelon stage is from: http://www.eventhubs.com/news/2011/may/27/more-capcom-fighting-game-stages-reimagined/
Looks like all the rest come from The Last Blade series except for the Nude Palace from SNK Versus Capcom: Chaos.
I want to put a bunch of original stages into Marvel Versus Capcom 4: Apex, and I am going to choose the MP3s myself. I would like somebody to recommend a set of original stages that do not have any music officially selected for them.