Scrap Metal

7 on Normal (9 on Joe Must Die, 5 of them by the Quarantine Area 2 Shed): Paddle Boat Deck (crate E), 2F Main Passage (inside the duct), 1F Main Passage (floor NW), Quarantine Area 1 (on the upturned bathtub of the Stilt House Underside and on the Lake's E platform) and Quarantine Area 2 (Central Walkway and Northern Walkway).

Scrap Metal + Tree Branch = Throwing Spear, the thrown spear. A spear to the head kills a normal or crawling Molded, and it is the only thing that kills alligators.

On top of the 18 spears placed on Normal, this gives at most 7 more.