I understand that ICAO and EASA are planning to build global repositories of aircraft accident reports, but at this time they are not available yet.
For the time being I use this "Virtual Library of Aircraft Accident Reports"
Linking Air Safety Investigations
(see query form at the bottom of the page)
It is a search engine based on "smart" Google search string so that the results of the search are almost exclusively Aircraft Accident Reports in .pdf format archived anywhere on the Net.
Give it a try!
NOTE: it does NOT work well with Internet Explorer, so use anything else, such as Firefox, Chrome or Safari.