Vectorsaur is the Vector stone evolution of the Venasaur starter on Pokemon. Vectorsaur can only be obtained when you have completen the Pokemon X and Y league and have won a vector stone from the random item machines located in the pokemon centre.
Vectorsaur can be seen in the pokedex if you battle a guy called Marvin around Route 56 after you have finished the pokemon league. Marvin will have Pokemon that can only be obtainable from the new range of stones.
If you breed a Vectorsaur it will make a Balbator which Balbator cannot evolve. Nintendo added this in as a 'special' pokemon which no other one from the new range of stones can do.
Chance of Obtaining Vector Stone: 1/200
Item Machine Cost: 50,000