I have done some work with the Charter Schools association in Minnesota. There are a LOT of them. This is the MN Chater Schools Association Website,
http://www.mncharterschools.org/ They should be able to point you in some direction if not help you out right.
There are also a few Private schools, but I don't know too much about those. I know there is a big disparity between cost and religious affiliation and the like. I don't have children of my own yet, so I'm not really plugged in to the HS community.
Now, if it were the Chicago Metro area, I know lots about that. I lived rather close to IMSA, so I know what you're talking about.
Mike