Patch 2.7.5 created a new NPC merchant called War Research and reinstate the Enchantment Rune purchases for Alliance Points. Previously, the Akaviri Motifs and style items were sold by the siege masters vendors. Recently, Gladiator Proofs were added to the game which allow purchase special runeboxes from these vendors.
War Researcher vendor in the base camps of Cyrodiil. War Researchers sell Akaviri Motif chapters, and the Style Items for Akaviri and Alliance styles.