Watch List for Low Level Blogs That Are Used as a Source for Higher Profile Publications

Why?

Online news publications need constant content 24/7/365. They often keep watch on low-level blogs and use materials they find there. It would be good to be up to date on which blogs they use often.

How?

Do a constant crawl of these high-profile publications to discover their sources, and keep an updated list of these sources ordered by topic and probability of being used as a source.