I'm afraid I don't know about any AC-specific lost and found at YVR, but (if this is of any help) the
YVR website states:
The YVR Lost and Found Department is located at the Customer Service Counter on Departures Level 3 of the International Terminal. Hours of operation are from 9:30 a.m. to 18:00 p.m. daily. The phone number is 604.276.6104.
There is also a World-wide Toll Free service available by dialing 1.866.817.5243.