The Seraph Bunkers are no longer available in the game as they were related to the seasonal activity during the Season of the Worthy. I take it you need to run a Legendary Lost Sector for the Solstice Armor. Bungie added Legendary and Master Lost Sectors to the game at the start of Year 4 - There is only a set number of Lost Sectors that have these difficulty as an option (Currently there are 13) - They are on a daily rotation with one Legendary and one Master - You will need to have completed the particular Lost Sector at least once on your character before you are able to select the difficulty options List of Lost Sectors [spoiler][b][u]Europa[/u][/b] - Concealed Void - Bunker E15 - Perdition [b][u]Cosmodrome[/u][/b] - Exodus Garden 2A - Veles Labyrinth [b][u]Moon[/u][/b] - K1 Logistics - K1 Communion - K1 Crew Quarters - K1 Revelation [b][u]EDZ[/u][/b] - The Quarry - Scavenger's Den - Excavation Site XII [b][u]Tangled Shore[/u][/b] - The Empty Tank[/spoiler] At the time of this reply, K1 Logistics is the current Legendary Lost Sector. After today's daily reset [July 23rd], K1 Communion will become the daily Legendary Lost Sector.