Repto is mentioned twice in How to Speak Dragonese, both times as dishes served to the Fat Consul. They have been neither seen nor mentioned since, so nothing is known about them.

"He was eating a light snack of double reptoburger with tomato-and-dormouse relish and popdragons on the side."
―Meal of the Fat Consul in How to Speak Dragonese

It is possible that Reptos were not meant to be a specific dragon species at all, but rather referring to a burger made out of Reptiles (which dragons are considered in the Books).