You might try Carnitas Don Alfredo in Melrose Park -- I had a pretty good tamal de elote there a couple months ago (see picture in this thread:)
viewtopic.php?f=14&t=32121&p=379405I'm sure they are experienced in large catering orders for carnitas, so they may be able to handle your large order of tamales as well.
Carnitas Don Alfredo
2501 West Lake Street
Melrose Park IL 60160
(708) 338-0844
Lacteos Santa Maria on 26th Street usually has them, but frozen. I don't know if they would be able to provide freshly made ones or not.
Lacteos Santa Maria
3424 W 26th St
Chicago, IL 60623
(773) 277-1760
Good luck!