In the past, the only way to find news from a specific source was to enter [Source: SiteNameHere]. Now you can use a site command, e.g., site:searchengineland.com at Google News, to pull up all articles Google News has in their index from this site.
In addition, you can search on partial names of the source. For example, all sources that start with “search engine” can be searched for by source:”search engine”; note that case matters.
A neat new feature on the Google News Advanced Search page is the Source Suggestions. Below is a screen capture of me typing “search engine” into the “News source” box, and Google showing me sources that contain those words: