There's quite the list of artifacts in the 6th Edition Lizardmen Army book for WFB that would work well as inspiration here, including adaptations of the sacred plaques the Slann could take.
These are most of them as presented in that army book.
Sacred Plaques (Slann only)
Cupped Hands of the Old Ones: grants accompanying units 5+ ward save against ranged attacks.
Divine Plaque of Protection: grants +2 bonus to ward save against ranged attacks
Plaque of Dominion: grants +1 dice for the old magic system (could be reworked into a casting bonus)
Plaque of Tepok: grants additional spell for the slann to use.
Magic Weapons:
Blade of Revered Tzunki: +1 Strength, no armour saves allowed
Scimitar of the Sun Resplendent: +2 attacks
Staff of the Lost Sun: 3 ranged attacks at Strength 5
Piranha Blade: unsaved wounds deal twice as much damage
Blade of Realities: (already in AoS), denied the use of ward saves, dealt twice as much damage to daemons
Dagger of Sotek: (skink only) Killing Blow ability, causes fear in Skaven
Sword of the Hornet: user strikes first
Burning Blade of Chotec: -2 AP, flaming attacks
Magic Armour
Sacred Stegadon Helm: (skink only) +1 armour save, +1 leadership (bear in mind that this was from well before seraphon were made into daemons with 10 bravery)
Shield of the Mirrored Pool: deflects back magic missile attacks on 4+
Maiming Shield: +1 attack to bites and shields
Enchanted Items
Gleaming Pendant of Chotec: (one use only) enemy units in base contact strike last in combat phase
Blood Statuette of Spite: (one use only) May freely cast a spell, must immediately make toughness tests until pass or slain.
Cloak of Feathers (already in AoS as one of the skink priest's options, allows user to FLY)
Charm of the Jaguar Warrior: increased movement to 9"
Curse-Charm of Tepok: (one use only) forces opposing spellcaster to re-roll miscast result.
Bane Head: nominates enemy character at start of battle to inflict twice as much damage.
Dragonfly of Quicksilver: +1 on Dice roll to determine who gets to deploy their scouts first.
Venom of the Firefly Frog: poisoned, magical attacks.
Arcane Items:
Rod of the Storm: magic missile 2d6 Strength 3 hits (4 if target has 4+ armour or better) within 18", unit that suffers wounds from rod must take an immediate bravery check.
Cube of Darkness: (one use only) up-scaled dispel scroll that affects all spells in play, ends magic phase on 4+.
Diadem of Power: Bearer can save up to 2 power dice for use in the following turn.
Now that I have access to my army book again, here's the remainder.
Talismans:
Amulet of Itzl: (one use only) 2+ ward save vs first wound suffered.
Aura of Quetzl: 4+ Ward save vs Strength 5+ attacks
Glyph Necklace: 5+ Ward Save
Magic Banners:
Totem of Prophecy: causes fear
Sun Standard of Chotec: Ranged attacks at user suffer -1 to hit.
Huanchi's Blessed Totem: (one use only) move 1d6" during the hero phase.
Jaguar Standard: additional d6" to pursue fleeing enemies
I'll even throw in the Sacred Spawnings, which could lend themselves towards unique takes on certain saurus-centric starhosts:
Blessed Spawning of Tzunki: Aquatic, +1 Initiative
Blessed Spawning of Sotek: (Can be taken by
SKINK HERO) +1 attack on the charge
Blessed Spawning of Quetzl: +1 to Armour Save
Blessed Spawning of Tlazcotl: Immune to psychology
Blessed Spawning of Chotec: roll an additional d6 when pursuing fleeing enemies, discarding the lowest result.
Blessed Spawning of Huanchi: May move through jungle, woods, and forest as if open ground, suffering no penalties for movement.
Blessed Spawning of Tepok: +1 dispel dice
Blessed Spawning of Itzl: (character only) must be taken in order to ride a Cold One or Carnosaur
Blessed Mark of the Old Ones: (unique, character only, can be taken by
SKINK HERO) may re-roll d3 single d6s per game, cannot be used to generate further re-rolls.