Your Action Camera Resource
These blog posts refer to Accessories for SJCAM models. Some of them fit all models including other brands, some of them are more specific due to the design of the camera (SJ4000 series vs M10 series).
The EKEN H9 camera as the exact same size as the SJ4000 & SJ5000 series, so these accessories will fit as well.
The underwater cases feature the same connector as the GoPros (GoPro mount), so you can use a wide variety of mounts.