I'm a complete n00b

I bought this HU used,
HU dimension: 178x176x50(mm)
But dash kit panel slot width is 190 mm.

click for larger pic

It's obvious that I'm missing an originally included surrounding "bracket" for the HU - will call to see if I can buy that part.

Now if they do not sell that part - what options do I have ? are there fitment brackets for this purpose ?

(car: 2004 Acura TSX)