Umm, I used to get them from Planet Renders. Then I discovered a site called Anime Render. It has some very nice renders, the only problem is you have to make 25 posts before you can see them, and 150 before you can see the really good ones. But 25 isn't that much.
But come to think of it, I'm pretty sure I have seen that render in Planet Renders before, so it's very possible you've seen it xD
Where do you get yours from?