This FAQ should provide the various links you may be looking for all in one place. As YodaMan said, if you have additional questions or concerns you'd like to raise privately, please feel free to send me a PM.
Originally Posted by Grizzgolf32Head to the Specializations Officer and they should have a series of side-objectives available for you to unlock the Gunner.
How do I get the mini gun?
Owning the Year One Pass circumvents the need for these side-objectives, and they will grant cosmetics instead.