I know what you mean. A few I have planed I know there is not going to be any game art for them. The OCD in me wants it all to be perfect even though I know it won't be the case for some of them. No I never heard of that site but will check it out, thanks. I mainly just use Google Image for the background image/s and to look for an image for below the text. If I find one I like I sometimes use
https://www.tineye.com/ to see if I can find a bigger or better quality version, although it doesn't always find the image.
One other thing I'm worrying about is some game covers won't fit well. I don't really like cropping too much from the retail art, but some of them just won't work. I'd like to use the retail cover art instead of a custom image, but trying to fit a vertical image into a horizontal space isn't easy. The main reason I did Rygar the way I did is because I didn't want to crop too much for it to fit and resizing it "smashed" it. I have Fester's Quest on my to do list and not only is the entire cover one big image, there is a Nintendo Seal on it as well. Not only is it not going to fit well, that Seal is going to be hard to remove because of where it's located and what's behind it, you can't just cover it up with a solid color.
I mean, I could crop the top right below the logo, move/resize the logo, but there is the Seal and other text still there and cropping that off would only leave his face and that would just make the image stretched having to resize it to fit.

I really like these covers, but after making some and planing to do others in my collection, these type of issues has made me reconsider using them, I just don't know.