What type of plastics are you seeking? In Elmhurst you have "It's Good to be King" and Al's Hobby Shop. Al's has Airfix, Hat, CTS, San Diego, Ilateri. King has San Diego, Britains, BMC, New Ray, etc.
The Olde Toy Soldier Shoppe is a great store, especially if you are into Britains, K&C, and various other metal toy soldiers. Whenever I am in the Milwaukee area I stop in and see Paul Hermann.