Big archive of Flipnote Studio [DSi] .PPM files.
Most of these are from about 2010
For playback, go to http://flipnote.rakujira.jp and drag a PPM file over.
Source of PPM's:
https://www.reddit.com/r/3dshacks/comments/6d5by5/do_you_have_hundreds_of_saved_flipnotes_from_your/di2g9xw/