Hi Newworld:
One place to start your search is our Venue listings here: http://www.marriedinmilwaukee.com/milwaukee-reception-halls/. You can sort these by capacity so you can look for places that can accomidate 250+.
Off the top of my head, I'd say these are some of the more-unique places:
- Mitchell Park Domes
- Lake Park Bistro
- 1451 Renaissance Place
- Villa Filomena
- Milwaukee Art Museum
- Humphrey Scottish Rite Masonic Center
- Lakefront Palm Garden
Best of luck with your plans!