I want a bracket to hold my box

Hi guys, i have my tv wall mounted on a fully movable bracket. When i was on holiday i seen they had their box sitting behind the tv in another bracket which was attached to either the back of the tv or the original bracket itself, i didnt really look too close to see. This is what i am looking for but i have checked in currys and argos but neither had such a thing. Anybody know where i might get one?

I was hoping for something that would completely hide the box at the back of my tv but some of those look ok thanks