Here's where players can turn in their Mark of the Spelunker Supreme and Web-Wrapped Curio omni-tokens in The War Within Season 1.
There are 3 vendors that sell Tier Set Armor in exchange for a Mark of the Spelunker Supreme or Web-Wrapped Curio: Ab'xal, Ip'xal, and Kir'xal. These vendors are located in City of Threads of Azj-Kahet.
Omni-Token Vendors
Ab'xal sells Tier Set Armor on the Champion Track in exchange for a Mark of the Spelunker Supreme. This vendor is mainly for PvP players because all of the Tier Set Armor from this vendor increases to a 639 item level when in Arenas and Battlegrounds. If you strictly play PvE Content, DO NOT PURCHASE TIER SET ARMOR FROM THIS VENDOR.
Similar to Ab'xal, Ip'xal sells Tier Set Armor on the Hero Track in exchange for a Mark of the Spelunker Supreme. This vendor is for the PvE-focused players because of the higher upgrade track and item level.
This vendor sells Tier Set Armor in exchange for a Web-Wrapped Curio that drops off Queen Ansurek in Nerub-ar Palace. The item level of the armor is based on the Raid difficulty that the Web-Wrapped Curio was obtained from.