I don't know what the situation is like at your local post office, but in my town I would simply ask to see the postmaster and explain the predicament. He/she may be able to do a little digging for you. Go back to the PO you shipped from, as they would have the best starting access. If you didn't ship it priority, a big package like that could be moved from truck to truck until it gets to its destination, adding days to the trip. Personally, I use USPS for smaller boxes only; that's their specialty. Good luck.