There is an inventory of naval stores from 330 BCE, Athens
https://inscriptions.packhum.org/text/3849?hs=11015-11029

Line 321, among the various armaments in the arsenals, it mentions

"Of lead bullets (molubdides) and lead in the wicker chest, weight 6 talents and 3 mnas"

That's 156 kg in store, so enough to cast maybe 5200 bullets. Nothing to sneeze at, though probably short of the quantities you'd need to equip a large contingent of slingers.

5200 balls of 30 grams.
But the text doesn't specify whether it is to equip specialized slingers or if it is small gun fire during naval battles. In the second case, it could be part of the arming of a warship.
Last possibility is the stock status during the inventory.
Thearos, your text is interesting. Because it is a big question. Just my idea.

Yes you're right, it could be for a catapult on a ship. Also ancient ships could use lead as anti-ramming devices (weights on yardarms to drop on enemy ships).

Thanks Tombelaine !