It could be just "Dracōnēs sagittāriī"
If you mean Dragon's Archers/Archers of the Dragon it would be "Dracōnis sagittāriī"
Or if you mean Dragons' Archers/Archers of the Dragons it would be "Dracōnum sagittāriī".
Note: both terms of any of those three sentences may be used in whichever order you like.