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".
As an alternative, it could be just "Dracōnēs sagittāriī", dragon-archers or archer-dragons.
Note: both terms of any of those three sentences may be used in whichever order you like.
