Are the new perks in Dead Money added to the general pool of perks, or do you acquire them as part of a quest or as another achievement related reward?

I got this perk through the normal perk selection on level up. I hadn't visited the dead money area yet either. You should be able to see it and the conditions to getting it in the pipboy when you go to choose a perk on levelup. It's a fun perk but I wont be picking it again next time.

Excellent, thank you. That was exactly what I was wanting to know. I take it you didn't enjoy the perk? If you don't mind me asking, what did you not like about it?

Maybe it feeels too powerful for him/her(it?)?

With Cowboy you don't need anythings other than a Lever-action shotgun.

I prefer my enemies to stay standing so I can finish them off quicker. There was time wasted in combat with multiple enemies as well thinking someone was dead and they weren't so it's not a perk I would choose again. Although it is a fun perk watching your target fly backwards like they do.