Go to "custommadeboxes.com". I had a similar circumstance as you but needed a pair of boxes made. They were quick, reasonably priced, shipped with the box broken down to minimize shipping cost, and are willing to make custom orders of one box only if necessary. Many of the custom box makers require a large lot, but not this company. I also found them very friendly and responsive to deal with. As long as you have the original foam inserts, you should be good to go. Good luck.
Where Can I Have a Box Made for Speaker?
I have a pair of speakers and only one box for one of the speakers. The other box had to be thrown out after a basement flood. So now I'm short one box. Do you know of a company that would make me a new box? I could provide the original box and packing as a template for a new one. By the way, the company (Mirage) is no longer in business, so I could not turn to them for a replacement.