Dragonite @ Scope Lens  
IVs: 14 HP / 24 Atk / 26 Def  
- Hidden Power [Flying]  
- Surf  
- Thunderbolt  
- Ice Beam  

Heracross @ Leftovers  
IVs: 6 HP / 24 Atk / 24 Def  
- Counter  
- Curse  
- Megahorn  
- Earthquake

Blissey (F) @ Leftovers   
- Counter  
- Curse  
- Rest  
- Double-Edge  

Dnite handles most Grounds, Grasses, Steels, and Vaporeon, Heracross guarantees most Electrics, along with beating Psychics, Normals (Though Tauros can still be a little shaky), and Tyranitar, and Blissey handles the remaining threats for the team like Gyarados and Articuno.  The only 3-0s I've found has been Ice Move + Water Move Vaporeon (though I might be wrong), and Leer HP FLying Dedge Hyper Beam Pink Bow Tauros.