About sci-fi cover art

For some time now, I've been toying with the idea of making book covers using classical art. I enjoy looking at images and playing with them in my image-editing program, Paint.net. I I also have a pretty big digital collection of large-size classical images. Their expired copyrights make them ideal as book covers for historical fiction of all kinds: romance, mystery, fantasy, adventure, biography, you name it. I even put up a post on my website that I'd do covers for free. So far, no one asked, but I hope someone will.

Unfortunately, I can't use any of the copyright-free images of classical art for a sci-fi story taking place on a space station. I have written one and am looking for a free cover art.

Does anyone know of an artist who would be willing to create a sci-fi image for free? As I'm not going to sell the story, just put it up on one of the free-read websites, I can't afford to pay. There are a couple of free image websites, and I scanned them, but I haven't found what I like.