Dull Coat will work however it's a laquer whereas your black is an acrylic. You need to let the acrylic THOROUGHLY cure and then spray your laquer on in very, very thin coats with ample curing time between or you can dissolve the acrylic. An acrylic flat coat such as Poly Scale or Model Master Acryl would be safer.
Alternatively, you can mix Tamiya XF-21 Flat Base with Future. The more XF-21 the flatter the appearance. A ratio of about 4:1 (Future:XF-21) gives a flat finish. Less XF-21 gives more gloss. More XF-21 gives a flatter finish, but also starts adding a slight white haze to the finish. This lets you adjust the gloss until you get the appearance that you want. Try it on some scrap first to make sure it looks the way you want it to.