Houses of Parliament Debate speeches
Dig around the Houses of Parliament "Hansard" and you'll find statements and speeches made in both the House of Commons and the House of Lords. You're bound to find some on a topic that interests you. They are great for practicing the techniques required to present without slides. https://hansard.parliament.uk/
Ted Talks
The presenters of Ted Talks memorise their scripts. They also get specialised coaching and practice for weeks! The great thing about Ted talk transcripts is that there is also a video of the actual presentation so yo can compare your attempt with the expert. https://www.ted.com/talks