Here’s a link to the ifixit GoPro Hero4 Black LCD Screen Replacement guide. The LCD and midframe assembly part is available from ifixit. Unfortunately the LCD only spare part is out of stock.
Here’s a link to the ifixit GoPro Hero4 Black Lens Replacement guide. Unfortunately the ifixit part is out of stock but here’s a link to a supplier of lenses for your camera. It is only shown to give an idea of the cost of the part. There may be other suppliers online that may suit you better. Just search for GoPro HERO4 Black lens part to get results.
Here’s a link to a supplier of the battery door part. I couldn’t find one in black. You may have better luck. Again it is just shown to give an idea of the cost of the part.
Hopefully this is of some help.