My uncle is very good at impromptu examples. He doesn't really know this, or know that I know this, but it's true. And I know because he's my pastor. Pastors love examples and use them in sermons all the time. My uncle loves historical examples. In fact, one of his best ones is... wait a second! I'm not going to tell you! You'll steal it! Anyway, unfortunately I didn't realize his knack for amazing impromptu examples until my impromptu career ended for the season. Darn. But now I know. So there.
I have a couple of go-to examples that I try really hard to avoid, because I love them, and they would be in every speech. Now I just try to have go-to categories of examples, and that's a lot better. But I can't say what those are, because you'll steal them. But I really like finding new good examples, because then each speech is brand new and feels good. Something else interesting to consider: finding amazing personal examples. This might sound kind of weird because, hello? they're personal. You shouldn't have to find them. I'm not a big fan of personal examples, but I get excited when I realize something that just happened to me could be used in a speech later. Recently I found a good one that could double as maybe an opener, but I can't tell you what it is because you'll steal it. Or try to. Or something.
Whether you're stalking the children's biography section at the library, taking particularly detailed notes from your history book or in a sermon, or just actually paying attention to the world around you, finding amazing impromptu examples is superfun. Of course, my favorite/best speeches are the crazy ones where I don't use any examples at all. (gasp!)
You're homeschooled, and you're probably not as paranoid as I am about people stealing your amazing examples.