Your best bet is to call a Realtor specializing in Streeterville rentals. There are a number of rental high-rises in the area, but there are probably an equal amount of individual owners renting condominiums as well. A Realtor should have access to both. If you would like, I can try to recommend an agent in the area.
If you want to try on your own, resources like the Chicago Reader and Craigslist.com can be very useful. The Chicago Tribune's website also tends to have listings for the rental high-rise buildings.
Hope this helps! Good luck!