I don't intend to be harsh, but I am a little ticked that somebody would even ask for such a thing. Why should an English teacher work for free? I mean, that's essentially what you're asking for. Teaching is a job, and even though there are many teachers who do love their work, that doesn't mean it's something they want to do for free in their spare time. If you want a native speaking teacher for your class, then do what every other school does and hire one.