He can contact the airline at YOW and see if they have the ticket and can somehow get it to him - that'd be my first step. If the airline has a desk wherever he is, go to the airport there and enlist their help (be conscious of time differences). If that doesn't work, he can try tr avelocity but I believe they'll be useless.

In the "old" days when paper tickets were common, I had to pay a $75 lost ticket fee where they searched to prove the original ticket wasn't used. There was a lot of paperwork involved as well and I had a lot of time before the trip in my case. I'm not sure if I bought a new one or flew on that itinerary to be honest. In your fathers I'm pretty sure he's going to be buying an identical ticket and hope when they process the lost ticket request he gets a refund likely for the original, not the new ticket cost.