Here are some options:
1. Ask your your PanelDue supplier if you can buy another cable.
2. Make up a 4-way cable with a 4-pin Molex KK connector at each end, and the order of the wires reversed between the two ends. You may have some 4-pin KK connectors left over from the ones that came with your Duet.
3. If the PanelDue is version 3 and the Duet is version 1.02 or later and the distance between the two is 300mm or less, use a 10-way ribbon cable. This is the easiest cable to make, and you can also buy it ready made on eBay etc.