At 50 miles you will probably never hear controllers unless you are on very high ground relative to ORD. But depending on where you are you may hear other interesting things (controllers for Chicago Center, for example, depending on where you are).
Many different scanners cover airband. You can just go on ebay.com and look for "police scanner" or you can buy new from many different sources. I highly recommend one of our partners Scanner Master
- they have a wide variety of scanners, antennas, and accessories.