I've seen them at Home Depot all spring long in San Diego County. I've seen both the white and purple fleshed varieties. In case you haven't researched these plants, they are a vine-like succulent plant that needs trellis support and full sun -- much like a grape.

Dragon Fruit grow on a semi-epiphytic cactus which needs a tropical climate to grow. Do you mean you want plants? Or are you just looking for the fruit?

Like Floral said, do you want to plant it or eat the fruit. If you are in the US and live in an area where there are Asian population, you can easily find dragon fruit in Asian market/grocery store. In fact, we find them in big chain supermarket like Stop&Shop, too.

If you are not in CA, but want to mail order it, try Logee's nursery in CT. They sell the plants on line. A good company.

Dragon fruit tastes mildly sweet. You should taste it before deciding to plant one, just in case you don't like the taste or texture.

I've seen on other forums that the white and pink fleshed varieties sold at HD are so-so in taste, but the red variety is not too bad. There are a lot of named cultivars you can find at local nurseries that supposedly taste a lot better. Hoping to get some of these soon to try myself