You can farm weapons that proc a damage shield and give those to your pet. Scratch that...quick search brought up no results. I seem to remember a low-level weapon that proc'ed a damage shield, but it has been too long.
Nothing out there to my knowledge. Damage Shields have decreased in importance, simply because the game's combat has increasingly scaled along damage mods and critical hits, which damage shields don't participate in.
ya, damage shields need to scale to about 10k per hit to be useful. Even a mage ds is less than 1% of the damage to a mob throughout the fight. They are kinda pointless.