Before you start first consider what types of organizations conduct research on your topic. If you aren't sure - or a number of organizations might investigate your topic - then using grey literature databases are a helpful alterative.
Use broad language to locate grey literature. When searching databases like Proquest you narrow and focus your search to limit your results. You do the opposite for grey literature searches.
Grey literature should be evaluated using the same standards as traditionally published materials. The following evaluation checklist was specifically created for grey literature to help judge the quality of the material.
A printable checklist is available for download at http://dspace.flinders.edu.au/jspui/bitstream/2328/3326/4/AACODS_Checklist.pdf