same problem, however here are some links to help you out,
Flickr is available, please please do what I do and that is to search under advanced and click the creative commons tab and also the commercial use tab. I also send a message to the author and send a link to the matte painting that I have done. If its a commercial matte painting I always ask the author. Never had a no yet, but I always keep a copy of their agreement on file.
Also do you possess a camera, if so use it, create your own texture library. Its hard to get organised at first but you will get the hang of it.