How central do you want to get? I can ask to host a get-together at Abe Lincoln Gun Club in Springfield, although I don't know that I could do it.
That would mean some restrictions--no targets that could cause ricochet, no full-auto or approximations thereof, and absolutely no alcohol or even empty containers on the property even after the guns are put away.
Darnall's in Bloomington is supposed to be great, and they do some really good defensive classes as well. Midwest Training Group is based there and they say they will do classes for groups on request, so if we could put together enough people we could do a THR shooting class. Bloomington is also very central, maybe even more so than Springfield.
The Buffalo Range is in Ottawa, which as observed above is not very centrally located, but it has the advantage of being a lot "looser" venue. They've got a "pit" area where you can shoot pretty much any target you want, for instance, and I believe they've got an area that's good for barbecue.
I haven't been there myself, this is just what I've been told.