Alliums are shipped and planted in the fall with daffodils and tulips. In your zone they may show up in nurseries in August ???

You may find some at your local nurseries this spring that are potted.

You will also find some as dry bulbs or bundled plants for spring planting. Depending on the hardiness of the species, if fall planting is possible, that generally produces best, but in those areas where hardiness is questionable or planting got missed last fall, early spring planting for most will still produce acceptable, if lesser, results. For ornamentals that are left in the ground, they will then produce results in future years indistinguishable from fall plantings.