Yes, been there, done that: you can mix any Tamiya Acrylic flat color with their acrylic clear (gloss), and you can end up with various degrees of sheen depending on how much gloss you mix in. However, I find it more convenient to spray the flat color on to the model first, and then when that has cured spray on the clear gloss, which may have Tamiya Acrylic Flat Base added if I need a satin sheen (or when simulating dissimilar panels). Putting on the clear gloss last creates a layer that protects the color underneath. The advantage of mixing the clear gloss with the flat color though is that you'll just be doing one painting session instead of two.