hehehe isn't it fun when you MUST get a hard to find item on a quickly approaching deadline?
I'd try a restaurant supply store if you have one in your area, or maybe somewhere like Michaels, AC Moore or IParty that sells party supplies and cake decorating stuff
Keep in mind that you don't need to run yourself ragged driving around from store to store...pick up the phone and call and ask if they have it before you hop in the car.
I actually saw some at my local Walmart recently. I don't think there were 24 of them though. Thank goodness there is a Walmart at practically every corner. You may have to drive around buying them all up!
I think I bought my last batch at the grocery store. Try near all the foil disposable pans. The ones I have are by Reynolds. I think there are 12 in the box.