I really think you asked two questions here. If you just want to improve your public speaking ability (Tone, inflection, stage presence) then Toastmaster's is a good place to get some practice and coaching. If a Toastmaster's is not near you then I would recommend recording yourself giving the speech by yourself and critic it yourself. Normally we are our own harshest critics.

But you mentioned to incorporate the art of selling from the stage, that sounds more like your need assistance crafting your message and how you want to portray to the audience the value you can provide to them. In that case, I would recommend starting with your current clients or prospects and gather from them what they feel you offer. If you have clients, can you find a compelling story of how you, your product or service helped them by solving a problem and what was the result of solving that problem? Then bring that story into your presentation.

Please feel free to reach out if you have any questions.