Once you get the Simple Workbench, one of the earliest things you can craft in Nightingale is the Simple Slingbow, which in turn will need its own ammo. And while you may be confused about where you can get it, it ends up being quite simple.
Where to Find Slingbow Ammo in Nightingale
Ammo for your slingbow can be crafted on the Simple Workbench. Slightly above the Simple Slingbow recipe, you can see the Simple Rock Marble, which requires only 6 Rocks to be made. The Marbles can be used as ammo, so simply craft a few of these to get your ammo.