Well I can tell you to buy them if you want, but I'm sure that's possibly not what you meant, even though that's what your question says. You can buy nasturtiums as seeds practically anywhere that sells plants - check what you're buying, they differ in size from 8 inches high and wide to climbing ones of 15 feet, but the packs will tell you. They're large seeds and they pop up easily - can be planted straight in the ground where you want them to flower.