As some manga fan, I should say I sometimes find a lot of weird stuff fans would make for their favorite manga, and in this case, hentai (or may be ecchi for "softcore").
So far I found, "doujinshi hentai" is never sold officially, but within the "circle" of the fans: By fans, from fans, to fans. (but some mangaka/comic artists (like Ken Akamatsu (love Hina)) make their own hentai doujinshi from their comic, in case the original comic is "softcore" enough)
And although may be Vince Sensei will not approve it (or will you, Sensei?
), what would YOU, the fans, say about it, just say if Class Menagerie is going to be very popular?
However, don't ever misunderstand this like I'm going to make one. But who knows, in a year or so? *naughty smirks*
*Runs for life*