Probably what you are looking for is not available. I've been looking for a song for a couple months and while the artist and his other songs come on, the one I want doesn't though it has before.
What I do when I get the awaiting sources is wait a bit, highlight the awaiting sources and click resume or find more sources. I bug the day lights out of LW but if you don't get results in a few hours, the song is not available when you request it.