Where do you find two-legged drifters?

[B2DMZ.KeNZo.]

I only found one near the Hammerlock's location, where's the rest?

[Itchy]

On the high plains

[Invocant]

You're already looking in the right place. They spawn mostly randomly. The quest log even mentions that all of those monsters are hard to find and only appear at certain times.

[Brodius]

Originally posted by Lockerxzx:

I only found one near the Hammerlock's location, where's the rest?

Just kill the same one you just killed; relog your game so you start at Hammerlocks place, if it is there then kill it, otherwise relog again and try again. Didn't take me long to get enough, this way.

[SinglePoorIan]

Keeping with tradition to trying to be like an mmo its a rare spawn so to complete the quest you have to clear the map. More than likely more than once.