been looking for this in ages
This is a tough one... All sources for this seem to be dead.
I at least found other Umineko doujins from this artist.
https://exhentai.org/g/207644/d8d797aaf1/
https://exhentai.org/g/243978/b1812d4d22/
https://exhentai.org/g/304288/ff6cd7ee99/
Best I can do.