Just to clarify, are you looking for a model of that nut or looking for a place to buy it? If you are looking to buy one then try searching for quarter turn t slot nut or rhombus t slot nut. I couldn't find that exact one but there are probably similar ones that would be interchangeable.
SS
Not to be a smart alec, but you could have drawn that in the time it took to post this--much less take those pictures.