Nurseries are stocked full with such bulbs, beginning in late summer.
Nurseries often put their bulbs on display several weeks before it's time to plant.
Check with the nursery staff for the ideal planting date and either wait, or go ahead and buy, then store the bulbs in a cool, dry place until planting time. Spring-flowering bulbs need a certain number of hours of cold temperatures in order to bloom. The six-inch soil temperature should be below 60 degrees before you plant them, which means the ideal planting date will vary considerably depending on where you live. If you miss the ideal planting time for your zone, you can plant bulbs as long as the ground isn't frozen. The later you plant, the later the blooms will appear in spring, and the stems may be shorter than usual.