On the shore, during the 1st act alone, there are random weapons lying around. Just head in a northeast direction, scavenge, and slay!
As the description states, you must of course kill the zombies with these weapons for it to count, simply hitting them will not do!
Examples of 10 you can find:
- Brass Knuckles
- Wood Plank
**Be sure to try different weapons (to assure achievement tracking accuracy), not variations of the same weapon.