Frankly, if I wanted matt black, I would just paint them myself, as matt black is the easiest color to paint... much easier than a gloss black. The key thing is to sand the chrome parts of the grill with some fine sandpaper (220 or finer), and use some appropriate primer. If you paint them yourself, them you can easily re-paint or touch them up with a perfect match if you get stone chips later, which you would not be able to do yourself if you have them professionally painted.

Can u Paint Plastic Chrome Grilles? - Kustom Kulture Lounge -=KKL=-

On the other hand, if you don't mind the cost and inability to retouch/repaint chips yourself, there is no doubt a professional painter will do a better job.