I tired out a couple of methods, but the one that worked for me was posted on youtube and goes as follows:
Run through Dead Air, chapter 3 on easy with 3 bots to the safe room at the end. Instead of going in and closing the door, however, grab the M-16, heal, and/or reload as needed and go back outside to the long hallway. All the bots will wait in the safe room.
Now camp about 1/2 way down the hallway. Every 15 seconds or so a special infected will spawn at the end of the hallway. If it's a boomer or a smoker, just kill it, but if it's a hunter just line up your shot and fire bursts over his head when you think he's going to jump. If you are at the right distance you get two jumps, and if you screw it up you'll get a new hunter in about a minute... it took me three to get the headshot.
The best things about this method are: 1) You have time to line up your shots, and he comes straight at you so it's easy, 2) If you get pounced the bots will run out, save you, then go back in the saferoom, so they never steal your kills, 3) If you really screw up you can dip into the safe room for additional ammo and health packs then go right back out to continue camping, and 4) Endless targets in rapid succession but NO normal infected or tanks EDIT: Do'h, apparently you can get normal infected, but not that many (relatively speaking).