Check out when your local tournaments are. You can usually get get discs a little cheaper (for cash) than you can at the stores. There is a tournament at Oswego this coming weekend (5th and 6th) and the merch man for it has a huge selection of Innova, Discraft, and Gateway. Plus Fade bags, stools, tshirts, hats, and all kinds of goodies. Best times are usually between rounds but you can buy stuff anytime. Between rounds are generally 10am-noonish and 2-4ish. You can get some solid help with disc selection then as well. More than you would be able to get if you were there during round set-ups. He is usually set up around 7am too.
There are a couple gas stations, 7-11s, and stuff in the surrounding areas that carry discs. You won't get the same selection as the tourneys (especially Illinois Open Series (IOSs) or Chains or A2B Boardshop (in that order). I haven't found anything in Woodridge yet though. Closest is Lombard that has more than a couple odds and ends. Midwest Disc Golf is not a store. It's a guy, more or less. You can run into him at the Lombards doubles usually.