What about the Stone Idol? Construction Six, E2S2 constant priest 3 prech that only work against dominion? It's very helpfull for dominion victory, although it's a tad pricy.
It's there under the "Very powerful items". It's especially pricey for Arco because you'd have to either empower a mage or forge another item to increase their paths depending on the picks you get, but it is among the best means available for a dominion kill.