Issued by agencies, corporations, government, departments, and research groups as opposed to mainstream publishers, grey literature fills in a lot of gaps that are not covered in the regular literature. While it is often not peer-reviewed it may be the only place you find the information.
Finding grey literature is only half the battle, the next step is getting your hands on a copy.
Another tactic is to search for more articles by the author of the paper you found. Sometimes people will issue a couple of conference papers or technical reports before finally getting the work assembled and published in a mainstream journal.