Then you need to up your game, Anon. Don't worry, I'm here to help because there is nothing more infuriating then someone asking for source and inflating a thread count who didn't try hard enough when they just didn't know how to.
There are actually 6 places you can check before declaring a sauce is hard to find.
The first is the image name. All the major sites have a format. Remember the format and you instantly know what site is the culprit.
This link has no such format, in fact the original file for this picture is the artist's blog.
The second is: Google.
Which gets you nothing but...
The third is:...archive links. Someone may have asked for this exact picture before or mentioned the artist, so search for the same image in the archive.
The fourth is IDQB. It links you to all of the front end Japanese major image sharing sites.
The fifth, which can be used very easily using IDQB, is SauceNao, which tracks sites like Pixiv which otherwise would be invisible.
The last is Exhentai's image search.
Why this boring lesson? Because IDQB had the answer all along (Danbooru/Gelbooru Repost), and led me straight to the artist's blog with the info they gave.
Have a nice browsing of 4chan, anon!