Hey Beaker,
Usually boxes for items as old as a 5500 aren't still available. However, the 7000 series components are the same size, and your dealer may still have those boxes available. Also, I wouldn't say that the original box is always the best way to ship the item. Personally, I'd wrap the item in bubble wrap and place it in a box with peanuts. Then I'd put that box into a slightly larger box with some more peanuts in it. The shipping price may then cost more with it double boxed, but at least you wouldn't have to pay the dealer for one of their boxes.
Austin