There is an event that you can do at Renown Six with Undermine and have signed a contract with the Blackwater Raiders that will cause Voltstrike the Charger to spawn.
Level scaling: Most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.