Newcomers to the lower latitudes are often surprised when the onions they brought from temperate climates fail to form bulbs. Onions are very sensitive to day length.
Most temperate onions use long days as a signal that it is time to form bulbs.
In the tropics the days never get that long. When Dr. Lesley Currah worked with the Natural Resources Institute, a British governmental organization, she made available to ECHO's network several varieties of short day onions that NRI was using in larger scale projects at research stations around the world. This enabled ECHO to send much smaller variety trials to our network. By now hopefully some of those trials have been positive and you need larger quantities of seed. Perhaps you can save your own.