Ofieri crossbow is a crossbow in the Hearts of Stone expansion and comes in 2 forms:
Ofieri crossbow (relic)
This version is found inside the Borsody Auction House vault during Open Sesame!, in a chest next to the pillar with the pressure plate opening the secret passage exit.
Associated quest
Ofieri crossbow (master)
This version can be purchased from Dulla kh'Amanni, the Ofieri merchant in Upper Mill.