In regards to the Ben 10 TG, you could always relay them to the Palcomix.com that has been left so conveniently by the "artist" in question.
Of course, if you need the actual link to the comic, I'll PM you the link. If you don't already know, however, both the comic and the link are NSFW.
As for the other one, I know I have it in my personal archives somewhere. Hopefully, the name of the artist is still there.
[EDIT]
According to Hydrith of DA, the "astoroth" pictures were made by "Bookaki" (
http://bookaki.deviantart.com/).
However, he has taken his work off of the site and hasn't been active on DA for sometime now. Comments on the main page suggest the pics were taken down as early as 2008, but the actual date the gallery was removed is unknown.
Aside from rickroll10000's upload, I've only found a handful of thumbnails titled "th_school1_by_bookaki" and "the_school2_by_bookaki". Unfortunately, the thumbnails don't work.
I know it isn't much, but I hope this will be enough.
Good luck.