Just messing around with dates there seem to be a lot of flights available into and out of MHK to get to Miami in September. May require moving the exact day your want to fly around a day or two but overall seems like you will be ok.
EDIT: LOL, just realized you probably wanted to book for the football game. Yeah, you are almost certainly mumped. I can't imagine there would be any seats available on anything around those dates given the very few planes leaving MHK each day.