There are 9 keys to collect in the Grounds and only 7 are required to get the Ice Arrows reward. You need a different dungeon item to collect one key. That is, the fairy bow to get one, megaton hammer to get another, etc. One you have enough items to get 7 keys, you can navigate through the maze to get the Ice Arrows.
Exactly, I researched this before and this is what I came up with:
Note that everything that follows is without glitches.
I confirmed this myself:
2 keys require something to fight with (i.e. the sword)
1 key requires the Song of Time
1 key requires another key (the one in the room of locks)
2 keys require the bow
1 key requires the megaton hammer
1 key requires the iron boots
1 key requires the silver guantlets
So this means at a minimum you need:
1. bow and megaton hammer
2. bow and iron boots
The silver gauntlets don't factor into this because you would have to get the iron boots and longshot to get the silver gauntlets without any glitches (so it would be an extension of option 2). This means that you can obtain the ice arrows after entering the Forest Temple for the bow and then either the Ice Cavern for the iron boots or Fire Temple for the megaton hammer.