No, rainbow sharks aren’t rare. In general, rainbow sharks are quite common, and you can easily buy them from pet stores or breeders. However, rainbow sharks with certain colorations can be rarer than others.
The most common and popular variety is the red-tailed rainbow shark, which has bright red fins paired with black or ruby red bodies.
Albino rainbow sharks are less common. Some albinos can have milky white bodies and red fins, while some have a light, peach-like color all throughout their bodies.
The rarest rainbow sharks are those bred and sold under the brand name Glofish. Glofish rainbow sharks, which are selectively bred from albino sharks, have unusual colorings, such as green, pink, yellow, and blue. Moreover, their bodies also appear to be glowing, hence their name.