1. Where do you search? Google, APPSearch, PubMed, lots of others.
2. What words or phrases do you use? Look for better, more scientific terms and for "subject headings."
3. Do you follow links between sources? Scholarly sources cite earlier sources and are in turn cited by later ones.
These are 3 variables that you can control. It also, of course, makes a difference what is published and where and how find-able those sources are. Also, a news or web source may refer to a scholarly source. Dig for the primary source!