Draptors spawns along with the dragons draid on Muggy Plains. The message that is broadcasted when it happens is "The dragons of the Dragonblaze Mountains have descended to Zao to protect the lizardkin!". This raid is random, which means that it can happen at any time of the day. The chance is adjusted so that it can only happen once each day, and most often do, but there is also a chance that it doesn't.