Instant Legolas (5e Equipment)
From D&D Wiki
An instant Legolas resembles a quiver mounted on any sort of bow. It takes one minute to attach one of these to a bow.
A typical instant Legolas can hold 4 arrows, but they can only have 2 fins, instead of the normal 3. Anyone using a bow with one of these quivers attached may make an extra attack whenever they take the attack option. However, after firing 4 arrows you need to take the reload action. Additionally, the normal range decreases by 10 feet and the long range by 30.
A popular way to circumvent this is by attaching an Ammo Duplicator inside the quiver. These types, however, can easily cost over 10000 gp.