The set can be obtained by following these steps along her questline:
- Defeat Aldrich in Anor Londo; this will make a summon sign left by Sirris to appear in the Undead Settlement.
- Travel to the Undead Settlement and head outside the Curse-rotted Greatwood's boss room to find Sirris's summon sign.
- Answer her call and help her to defeat Hodrick in the Pit of Hollows.
- Rest at any bonfire and travel back to the Pit of Hollows to find the set lying beside the Altar of Sacrifice.