They're found abandoned all over. Once you start seeing them, there are lots. Sometimes they're left by ppls gas or by CDOT. I find them on the shoulder in the planned manufacturing district off 35th street. Sometimes they're down on the Bubbly Creek river bank.
I just had to run to my bank in UIC. Here we're two that looked pretty abandoned on the way. The one might be a dibs cone but I usually consider any cones in the Parkway where there is no construction to be up for grabs.
I also have a couple flex posts that I've found in gutters. If the base is intact I keep them. My wife is not always fan of my street artifact hoarding. Lol