Searching for books across all sources?

Is there a way to search for a book across all the sources (Amazon, Library of Congress, etc) without having to search each separately one by one? Thank you.

No. OverCat includes books from many library sources, but not all the books from those sources.

OverCat is the closest to it. It doesn't search various sources, but it does contain data from all library searches conducted on the site.