You Can Buy This Item from Amazon:

UPC: 716670913709

Bullet Point:

1) Compatiable with Gopro Hero 3+, Hero4 Standard housing case.
2) Easy-to-spot flotation attaches directly to the housing backdoor.
3) Protect the camera from sinking if dropped accidently.
4) Pefect for snorkeling,scuba diving,surfing,wakeboarding and any other deep water activity.
5) Package Includes: Standard Backdoor x 1,Floaty Box x 1,Adhesive Sticker x 3.

Floaty Backdoor keeps your camera safe and afloat while in snorkeling, scuba diving, surfing, wakeboarding and any other deep water activity,Remove your original backdoor and attach this Floaty Backdoor to your camera. Holds on strong in surf and waves.

Package Included:
Standard Backdoor x 1
Floaty Box x 1
Adhesive Sticker x 3