I have been trying to search for some writings of Winston Churchill regarding Africa and cannot find any quotes or links to those writings. I can't find any books with the compilations either as those writings were not flattering and the Left wants them buried.
Maybe you haven't been using the correct search terms. Actually, there's a ton of leftist mainstream info about Churchill's racism. This is just a small sampling.
The Guardian: Why can't Britain handle the truth about Winston Churchill?
Wikipedia: Racial views of Winston Churchill
The Conversation: Deconstructing the cult of Winston Churchill: racism, deification and nostalgia for empire
CNN: Yes, Churchill was a racist. It’s time to break free of his ‘great white men’ view of history
Washington Post: The dark side of Winston Churchill’s legacy no one should forget
New York Times: The Case Against Winston Churchill