Here I am sharing old technique but still its work great. Follow these steps & get some amazing free content !
First step - Find expired or deleted Domain, you can search it on www.expireddomains.net
Second Step - Search these domain on Archive.org, you will get entire website. Actually these expired website have lot of content which was indexed by google but now after expired, automatically become un-indexed.
Third Step - Copy content and check it on Palagarism or Copyscape.
Mostly you will find unique Content.