If you don't have any luck, you can try stores. I used to work at target, and we would give boxes to people who ask all the time. There is some stuff that comes in boxes that big, but not alot, so you would probably have to talk to a manager (or L.O.D. as we were suppose to call them) to save one for you when whatever item has to be stocked.
Give my brother (Keith) a call at Sideline Packaging 248.398.7256. His store is in Berkley but he said he can get the boxes to the Mt. Clemens are if that would help. His largest box he carries is 48" x 24" x 21". My brother can fit in the box. He is 6'5" 225 lbs. What the he!! he was doing in that box I dont know. He sells the boxes for about $13.00 but tell him that Jim sent you and he might help you out with the price.