The resources on this page provide a general starting point to searching for grey literature.
Here you will find links to databases that specifically collect and index grey literature documents. The search engines found on this page have been designed to conduct broad searches across global databases, including the deep web. The preformulated search strategies have been designed to filter for specific types of grey literature such as non-governmental documents.
As the scope of grey literature is extremely broad, Sayre recommends considering the following questions in order to narrow down your search http://www.slideshare.net/fdsayre/introduction-to-grey-literature-for-health-sciences - slide 8:
If you are conducting a systematic review, see Paynter's checklist of resources that covers three specific categories: regulatory information, trial registries, and abstracts & conferences.
The resources below contain lists of the many databases that can be searched for grey literature.