Instructions
Travel to Hyrule Town as young Link, or the Kakariko Village as adult Link.
Enter the Bazaar. In both locations, the building will have a giant picture of a bearded man over it.
Speak to the shopkeeper and press right on the analog stick to enter the purchase menu.
Select the arrows. Arrows come in three denominations: 10, 30 and 50 arrows, costing 20, 60 or 90 rupees respectively.
Purchase as many arrows as needed.