Establishing an adult pair can be a little tricky, and a close eye needs to be kept on them to make sure that the female doesn't kill the male. Buying a large adult and getting two smaller ones from a group and letting the female pick one is an approach that has yielded a good deal of success. With maroons, try introducing just one male at a time and keep a close eye on them. It takes patience to get them to spawn, and there are a few things you can do to help. Use a good quality live food in combination with a well rounded diet.
Fresh shrimp frozen and then grated is a good nutritional source.
Make them feel secure. Remove any aggressive fish that might make them feel threatened. Sometimes a good porno movie helps. Some type of filtration that will not harm the larvae when they hatch. A clay pot or a piece of ceramic tile is a favorite to spawn on.