I have looked a few times on craigslist for Pentax gear just for the fun of it because I live about 4 hours from Chicago. Now, I do not know if this person has a small shop or is selling out of his home but he has a lot of ads listed for all types of used gear including Pentax.
chicago for sale - craigslist
As with anything on craigslist, be careful about where you will meet and take a friend or two.
After looking at a street view on Google, I am starting to believe this seller is selling out of his house and Grand and Harlem is the closest big cross street to where he lives.