Maroon is unfortunately a pretty vague colour term, like burgundy, beige, olive, mauve and a bunch of others.
But you can get any of the range of colours you might be aiming for using:
Cadmium Red Medium + Mars Black;
Cadmium Red Medium + Burnt Umber;
Cadmium Red Medium + French Ultramarine;
Cadmium Red Medium + Lamp Black;
Cadmium Red Medium + Prussian Blue;
Cadmium Red Medium + a phthalo blue;
Cadmium Red Medium + a phthalo green.
These are in rough opacity order, from most to least.
Dioxazine Violet + an orange will also give you the right sort of colour, even violet + yellow can work, but they won't be as opaque so coverage might be a problem.
Einion