Finding and verifying quotations on the web

Try to use a proprietary database like LitFinder, if you have access to one. If you're stuck searching the web though, here's a way to improve your chances. Google your phrase or keywords, and add "filetype:pdf". This will exclude all the html web sources like Brainyquote and ThinkExist, which are not rigorously sourced. The resulting pdf files will often be from actual print publications, wherein you will have a better chance of finding a solid source. You can also do filetype:txt, which will net you online texts from The Gutenberg Project and similar sources.