Messenger jobs are far and few between. You may want to check out food deliver on a bike. Companies like Caviar or Uber Eats. Have you tried www.linkedin.com or www.indeed.com? Search google with any companies name + courier and see what might come up too.
I'm not sure how great your luck is going to be finding this sort of work, especially in a metropolitan area like Chicago. I used to live in New York City, which is similar to Chicago in many regards, and messenger jobs really weren't all that common.
The most similar, fairly abundant work you might be able to find is that of a delivery guy for restaurants or grocery stores. They're essentially messengers, but instead of information, they send delicious food! Almost all delivery people in my neighborhood rode bicycles.
Actual "messenger" work exists where I currently live, but it's because I live in a rural area where that sort of work is still required. Good luck on your hunt! Sites like Craigslist would probably be your best option.
I think bike messenger is really fun exciting job, specially if you're bike enthusiastic. But I think this one is not applicable in our country. without a bike lane and in tropical country. That's why it's really funny when fast foods hired food deliver on bike, the delivery guy is not presentable anymore and looks haggard because of the hot weather in our country.