What npcs drop the most arrows?

General
1

any arrow type is fine

2

Moss Giants drop 30 Steel arrows. (1/128) And 15 iron arrows (2/128)
White knights drop 2 addy arrows (1/128) and 5 mithril arrows (2/128)
Barbarians drop 15 bronze arrows (3/128)
Ice Warriors drop 2 addy arrows (2/128) and 3 mithril (5/128)

You can look at all drop tables here.