Grey Literature for Non-Health Subjects

Note that the number of hits Google reports is usually an overestimate. Page 1 of your results may say there are 150,000 results, when in fact there are only 400. 

Google Scholar can be useful for finding grey literature, but this 2015 study suggests that it shouldn't be the only source searched: 

Haddaway NR, Collins AM, Coughlin D, Kirk S (2015) The Role of Google Scholar in evidence reviews and its applicability to grey literature searching. PLoS ONE 10(9). doi:10.1371/journal.pone.0138237

Note that you'll need to take a different approach to building search strategies in Google and Google Scholar than in many other databases:

• Truncation/wildcard searching is not supported
• Google Scholar has a 256 character limit for searches; Google limits to 150 words
• Google and Google Scholar show only the first 1000 results
• Nesting terms in parentheses - eg, (science OR technology) AND (british columbia OR alberta) - does not work as it does in other databases

For more details, see:

Bramer WM, Giustini D, Kramer BM, Anderson P (2013). The comparative recall of Google Scholar versus PubMed in identical searches for biomedical systematic reviews: a review of searches used in systematic reviews. Systematic Reviews 2(115). http://doi.org/10.1186/2046-4053-2-115

Advanced search operators give you more control over what results Google returns:                           

For an excellent resource on searching with Google see the Google Advanced Power Searching page.