The OEM cable is Icom part number OPC-023C. You may be able to find one on eBay or at a dealer that has old Icom stock.
Or, you can make your own. Check at Radio Shack to see if they have a 4-pin Molex connector that matches the DC input on the back of the radio (between the fuse for the internal AC power supply and the antenna connector). Then get some 18 gauge or larger zip cord and make the cable you need.