Multiplier onions used to be a popular garden onion, but are now somewhat difficult to find. Their flavour is about the same as white onions, but they tend to store better. If a small bulb is planted, it will produce two or three large bulbs, but if a large bulb is planted, ten or fifteen small bulbs will be produced. The young greens are also well-suited to use as scallions.
Plant bulbs in early spring in fertile soil, and keep them somewhat moist for best production. They rarely flower, but cut off any flowerbuds that do form for the best production, and harvest when the tops die down. Cure for one or two months in a warm, dark place, then store in a cool, dry place. Save some bulbs of various sizes for replanting in the spring. Fall planting may be successful in warmer areas (zone 5, and possibly colder); experimenting with cold frames or mulch may give an earlier yield and bigger bulbs the next year in colder climates.
If you are lucky enough to know anyone that grows these, ask them for a couple bulbs, otherwise try ordering from Territorial Seed Company or Park Seed Company. The bulbs will probably not get as big as seed-grown types, but they are gaining popularity among people concerned with self-reliance and saving money, because seeds or sets do not have to be purchased once you have these bulbs.