Shipping boxes for mattress & box springs?

We are arranging to drop off some items for shipping on Thursday morning (it's now Tuesday afternoon), and our shipping company has just told me that we'll need to put our mattress and box springs in boxes ourselves, or they won't ship them. They suggested I look at U-Haul for those boxes, but they don't seem to carry them. Any idea where we could get these on such short notice? I'm a bit annoyed they only just now told me , and we don't have a car (or drivers licences) to go pick anything up.