OPI has a color called Bastille My Heart that I think is dark maroon.
My suggestion is to go to OPI's website. Click "Nail Colors" at the top, then pick "All OPI Colors" from the drop down menu. Scroll through the little swatches until you find one that's dark maroon to you. Write down the name and go to the nearest salon/beauty supply store and buy that color.
Like kmhco said every brand has different names for there colors, and they all vary in how they look. Sometimes it's just best to ask when you see a color you like on someone. Or you may never find it. Below are two nice brands you may want to look at.
Just look at the bottle, and if it is the right color then that's it. Every different brand has a different name for their colors/shades. You can go to the store and look at the bottle. It's a pretty good signifier of what the nail polish looks like.