It is not a quest item, though it may have originally been intended to be part of a quest which was taken out of the game.
There is an NPC named Stan listed in the data.000 file, located in the NPC storage area (see
Reviving dead NPCs for details). Teleporting him to my character's location, Stan is dressed as one of the bowman at the castle archery range (bow, blue and yellow tunic). Talking to him, he says he is out of arrows, but can not leave the range, and asks you to fetch some arrows for him from the general store. If you agree he claims to give you some money (didn't check that) and mark the location of the store on your map (no flag added).
You can also refuse, asking if you look like a simple errand boy. He says yes, that is why he asked but he would ask someone else. You then throw a fit, saying you are the lord protector and could have him hung for talking to you like that. He replies that there is no need to get violent, the way you are dressed you look like an errand boy, and apologizes.