Does anyone know where I can find a torrent for the movie?

http://www.ebizmba.com/articles/torrent-websites
this website has a list of 15 popular torrent sites, and with the help of a program like Vuze or uTorrent, you should be able to find and download almost any movie.

Also note that because Insidious is still in theaters, most copies will probably be poor quality from a hidden camera.