It depends on the options you installed because you could have chosen to have the items added to loot lists, so you would need to go track down baddies or find select chests to acquire the new items. Doesn't the ReadMe explain this?
Edit: I do not know if this helps, but here is an excerpt from the mods description at TESNexus
Plugins Explained:
Armamentarium.esm - core file of Armamentarium Complete. Don't try to run any other plugins of Armamentarium without this one - the game will crash before it loads. This file stores properties of all items. Weapons and armors are balanced to match those from Oscuro's Oblivion Overhaul mod. Vanilla users will find armors more costly and weapons more potent.
ArmamentariumArtifacts.esp - this file deals with quest and special items, and artifacts. All information about all these items you can obtain/buy from the new smith, Mercator Saccus, and his Chest of Requests in The Fightning Chance shop in the Merchant District of The Imperial City.
ArmamentariumLL.esp and LLMagic.esp - leveled lists for vanilla Oblivion. Add Normal and Enchanted Weapons and Armor If not using a Overhaul use this
ArmamentariumLL4OOO.esp and LLMagicOOO.esp - leveled lists for Oscuro's Oblivion Overhaul mod. Includes OMOBS Rebalance for Arma Items and If you have FCOM installed use these file.
ArmamentariumLLVendors.esp - leveled lists for merchants, use this file if you want to have some chance to buy wooden/iron/steel weapons and armors from merchants in game. for Overhauls
ArmamentariumLLArmaVendors.esp - use this file if you want more types up to elven and oricish armor and weapons from vendors in games, not for overhauls..
Artifacts-ArmaCompleteAddon.esp - requires Artifacts mod to be installed itself, adds nearly all weapons and armor from this mod into Armamentarium Leveledlist , considered a addon for ArmaComplete Once again. works with OOO/FCOM plugins listed above has well.