In DragonVale for the iPhone and iPad, the Sakura Dragon is a limited dragon that is only available in the Spring time.
To get a Sakura Dragon, you need to breed dragons together that have the plant, earth, and fire attributes in the Epic Breeding Cave. Obviously one of these dragons will need to be a hybrid dragon. Tree + Flower seems to be the only successful mix at the moment.
Check out my DragonVale Breeding Guide for more dragon breeding combinations.