Below are the photos of the ring adapter and holder which I bought. And I will attach the links too, but the pages all are chinese version. Hope you able to find the way to order it.
Adapter Ring
http://world.taobao.com/item/520220178381.htm?fromSite=main&spm=a312a.7700846.9.117.fb2jit&_u=i234sp735630
Holder
Holder with GND filter
But unfortunately there is still having dark corner at 45 degrees. But not a problem for me because I normally using 0 and 90 degrees.
0 Degrees
90 Degrees
45 Degrees
Here is the actual look which attach on the lens. Due to Ultra wide unable to avoid light leaking issue at long exposure(using little stopper/big stopper), so I was using the black cloths to cover on the back of holder. It work fine.
Attaching with Little Stopper and GND soft 0.6
Sample of the shots with both little stopper and GND soft 0.6.
Other shots with GND soft 0.6
~ END ~