A lot of services today allow Google to pass search query through them.
Maybe you could join your search with Google also?
So when I'll search Google for "sheetmusic over the rainbow", along the other results will be also "results from NoteFlight", showing the results from NoteFlight of course...

This feature will not only spread NoteFlight more widely, and will not only make it easier for people to find sheetmusic all over the world,
But it will also help composers to publish their music and receive feedbacks...