Hi there. You can try any major music bookstore. If I am not wrong, the yamaha school at Plaza Sing offers a superb selection of them. Alternatively, you can go download scores from http://www.popiano.com. There is this program (overture 4.02) which was once effective in opening scores saved as .ove format. All you had to do was to open it using overture and press play, and the song is performed 'live' with a cursor moving over the notes played in realtime. However, overture 4.02 appears to be buggy and with recent downloads, does not seem to be working.
As a sidenote, if anyone has a solution to overture 4.02, please post. Thanks!