You Can Buy This Item from Amazon:

Bullet Point:

1) Applicable models: GoPro Hero 5.
2) The Lens cap protect your camera lens from scratches,dirty and broken.
3) Made of good quality Silicone and fits your Hero 5 Camera and housing perfectly.
4) The Lens Cap only compatible with Gopro official camera and housing,not compatible with 3rd party housing.
5) Compatible with GoPro Hero 5 Black only.

Package Include:

1 x Lens Cap for GoPro Hero 5 Black Camera
1 x Lens Cap for GoPro Hero 5 Housing Case