The class specific swords are a "rare" drop from engrams. Personally I've gotten all them a few times (and at least 5 quickfang...)
If you want a guarantee, you can remake your Hunter. If you're sure to throw all your great into the vault, as soon as you hit 20 you'll be right back where you were... but with a Quickfang! That takes the patience to run back through the story.
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I do appreciate the input and tip. If ever I would find myself bored enough, i will!