Amazon.com: Freewell ND Filter Kit Includes ND4, ND8, ND16 and ND32 Filter (4-Pack) Compatible with Hero7 Black, Hero5 & Hero6 Black Camera : Electronics
Camera Butter Glass ND filter for GoPro Hero 5/6/7 (Choose Density)
Cinematic Motion with GoPro ND Filters - PolarPro Cinema Series Filter Review | CineD
Neewer Camera Lens Filter Kit for GoPro Hero 5 6 7: 4x Neutral Density ND Filter ND4 ND8 ND16 ND32 + 1x UV + 1x CPL Filter|Camera Filters| - AliExpress