I would eye through some of his speeches. A couple of english translations can be found here http://web.archive.org/web/20180524035711/http://www.olofpal...

This is probably your best bet. https://jacobinmag.com/search?query=olof+palme

The documentary about the Swedish involvement in South Africa is also fascinating, but not specifically about Palme. https://www.youtube.com/watch?v=_4Ah8HCRcrQ