There seems to be several sales going on for orbs for legendary dragons, ironically 5 of them are breedable but the list that I have is below all are 5 for 9 gems. Not sure how many they will allow you to buy though since I have no plans to buy any.
Liquid
Dragasand
Legacy
Witch
Winter Phoenix [VIP]
Kratus
Electrostatic
Rocket [VIP]
Abyss
Apocalypse
Forge
Enigmatic [VIP]
Cow
Alien - not legendary