You could try The Right Stuf. They sell the official art boxes separately from the DVD sets at about $15 apiece. I've purchased several from them, including the Bebop one. But I think the Bebop boxes are long gone by now.
the bebop boxes are not made anymore least time i check they were around $50 on ebay (note:only for the box) i think thats a waste of money but u could check ebay