Various clubs (Toastmasters is the most widespread one) can provide that. But don't discount the benefit of preparing a speech and delivering it over and over again, even to no one. Filming yourself can provide the feedback component.
I think "Thank You For Arguing"  is a good resource on persuasion broadly. Some of the same things that work on a person-to-person level also apply to a speaker-to-audience relationship, and the book goes into both areas.
American Rhetoric has a library of audio recordings from "great speeches" . Listen, and imitate the things you like.
Finally, more than anything else, I'd actually recommend taking improv comedy/improv theater classes. They taught me two things: that not knowing what you're going to say next is totally fine, and that the audience is on your side and wants you to succeed. Knowing both of those things in your bones before you take the stage makes everything so much easier.
 https://www.amazon.com/Thank-You-Arguing-Revised-Updated/dp/... http://www.americanrhetoric.com/top100speechesall.html