Is there a good Asian supermarket with a fish counter? I would go there and ask them.

Otherwise, check out any good fishmonger.

I'm not a local, so I can't give you any specifics.

you can buy fresh squid at a lot of places in chicago, try china town market or ktown, I think i saw it at fox and obel too.

harvest squid ink
http://www.instructables.com/id/How-to-Harvest-Squid-Ink/

If you live more towards the suburbs or are willing to make a trek via the blue line and pace bus 606 you can go to Mitsuwa the areas largest asian market. I have seen it there before. You can also check out all their other goodies and their awesome food court!

Try Dirk's Fish Shop on Clybourn - dirksfish.com
I've bought whole octopi from them. If they don't have it, I bet they'd know where to find it.

Squids. You're welcome.

J/K, our local intl. market has it on occasion. If you don't see it there, ask! They might know how & where

Asian markets also always have squid frozen in 2 or 3 pound boxes in the freezer section if you can't find fresh squid. Just defrost, use the squid for something else, and cut open the ink sac. It's super cheap. Here in CA those boxes are maybe $4 for 2 pounds of squid?

If you do this you have to clean the squid as it is frozen whole, which I never mind but some people don't like. It's easier if you can find fresh, cleaned squid though.

Online:

LaTienda.com sells 8 x 4gr packets of squid ink for $9.50, shipping is a flat $8.95. They also sell a large jar for around $36, but shipping is still the same.

A good fishmonger or your local fish market should have it. Asian cuisine does not use squid ink (it's considered a waste product, and, being black, is a bit scary) so I would be surprised to find it at an Asian market. Also, the squid sold there has normally had the ink sac removed.

If you're not keen on going to the 'burbs, or don't have a car, the Joong Boo Market in Avondale may have it. http://www.joongboomarket.com/index.php