Unlike previous Uncharted games, there is no infinite enemy spawn points.
For this one, load up the game on easy and enable the one hit kill and infinite ammo tweaks. If you start from chapter 1, you'll get this around chapter 6. A "faster" method would be to load up chapter 20; starting from there you'll get it in chapter 22. Beware, the "fire demons" in chapter 21 still require 2 hits to take down, even with the one hit kill tweak on.
Fortunately, there is a bit of a work around if you accidentally die. As long as you quit to the main menu before the game re-spawns you, you can select continue and your streak will not be broken.
It would be wise to stack this with Side Arm Master and Reload Master as well, to save yourself some time.