Fresh cut poppies last only a couple of days, so it is unlikely to find any at a florist. But there are many reputable online nurseries that sell poppy seeds. Burpee.com, whiteflowerfarm.com and bouncingbearbotanicals.com are a few sellers that guarantee their quality of seeds.
Each of the site gives specific information about the different varieties of poppy seeds that they have for sale, and they provide specific growing instructions. For example, burpee.com sells Oriental Poppy Mix, which is an heirloom mix that produces hardy plants that require little care. Opiumpoppyseeds.com sells Pacific Northwest Poppies that are rare and hard to find. The company guarantees its germination rates at 90 to 95 percent and has been growing and producing these seeds for over 10 years.