Baby Fairs/expos

I think the main ones are in August and November. You can find some on the site for Chicago Parent Magazine and search "expo". There is one coming up by the Academy of Pediatrics.
•10 a.m.-6 p.m. March 8, 10 a.m.-4 p.m. March 9
•Donald E. Stephens Convention Center, Rosemont
•Advance registration $8, $10 at the door; free kids.
•healthychildrenexpo.org
•Sessions in English and Spanish. The website also offered in Spanish
There is also a pet expo in March at Arlington Race Track.

I'd suggest you edit the title to list the region you're looking in, and then indicate in the question whether you are looking to attend, or to get a booth for your own wares. People in your area will want to know what you're looking for.

You might want to google your area. I know they are usually in the spring around here.