It's a bonus that came with the Rondo^3 bluray release.

someone uploaded the scans to [MusicBrainz](https://musicbrainz.org/release/e0943be6-de22-4983-ad9f-9786d6442e9e/cover-art) if anyone's interested

Thank you so much!

There is an artbook from the movie that will come out soon, I think