I have no idea about an IRL analog of what Malfoy has, but I’d recommend the book The Charisma Myth (in addition to, not instead of lsusr’s suggestions), and all types of acting, not just improv. Improv may be great for overcoming shyness and other mental blockers, but acting from a script and inhabiting a character lets you try on vastly different ways of experiencing the world. Playing a powerful and/or confident character won’t teach you negotiation skills, but if done right it will teach you the body language of a powerful person and what it feels like to have that mindset.
I mention this because people are really into recommending improv, but I personally have a crippling fear of improv even though I love being onstage. If that applies to you too (the general ‘you’, not just shenkev), then don’t think that all of the benefits of it have to be closed to you – you can get a lot of the same out of normal acting.