Those cables used to be easy to find on ebay but that changed when a huge load of M7300s hit the surplus market recently, which did not include power cables with them.
I've got a few used short power cables. 2 to 6 feet in length.
When I need them to complete an M7300 radio kit that I sell, I only provide new cables. Yeah it costs more, but I won't take the liability of selling somebody a power cable that has a splice in the middle of it, which can be a fire hazard.