They probably have it but I am not sure. There is a connector that plug in to the car harness for after market radio. This one is easy as every place has them. There is also a connector for using stock radio in different car. This one is a PITA to find. I know they have one for Toyota (86-90 cars). When you find the 2, connect 'em together to make an extension.
Your other option is go to junkyard and get/cut/chop the "To-HU" end from the same car or different Honda (if it the same as yours). Now buy the "to-Harness" end and connect them together.
Another option is cut your car harness and make the wire longer, but I am sure you dont' want to do that.