As Opera is an acquired taste not too many people are into exchanging videos of it on the internet. My advice would be to be very careful about the files that you do download and to always thoroughly scan them with your antivirus program before you click on them to activate whatever is being carried in that file.
Good luck in finding what you would like to view but I can honestly say there would not be many opera aficianadoes exchanging files via the internet. Maybe if you were to try actually naming the performance (Rigoletto, Barber of Saville etc) or performer (Pavarotti, Sutherland, Carreras etc) you are looking for might return better results than just putting a random search term like: "Opera" in the search box.