What an interesting question! It isn't a manga. Its credited on zerochan as being apart of an artbook for the mangaka Kauaki. If it is one, then it isn't scanned though.
http://www.zerochan.net/330978 (image source)
https://www.mangaupdates.com/authors.html?id=7266 (mangaka)
I've always seen that credit page for Girls Generation and wondered the same myself. If your ever curious on finding the source for an image in the future, just right click the image, click copy image location, and put it into google (search by image) and it'll pop up.
I'm both sad and happy with this reply Cx
Sad that it's not an actual manga but h
appy that I now know where to find it :P
http://www.mangago.zone/read-manga/ouji_no_kikan/an/165329/Vol1_Ch3/pg-3/ : Is this actually a manga and if it is does anyone know how to find it?!