Artifact cloak of invisibility Death’s Embrace, which grants phasing, immunity to death effects, and half physical damage, but reduces speed.

An unaligned artifact amulet versus poison which also confers sickness resistance, half physical damage, and raises Constitution to 25 when worn. Tentatively named “The Eye of [something]”.

Shimmering dragon scales or scale mail should grant half physical damage in addition to displacement because anything that hits you is likely a glancing blow due to the displacement.

Chargeable ring that reduces incoming damage (perhaps by half, not triggering if half physical or half spell damage applies from some other source) but may lose a charge every time you take damage.

The Heart of Ahriman grants half physical damage, and Thoth Amon is nearly guaranteed to pick it up.