Here's a recap. Hope I got the numbers right.
O = Opera (an opera scene in a movie)
1. Moonstruck
2. A Night at the Opera
3. The Godfather: Part III
4. Meeting Venus
5. Age of Innocence
6. Amadeus
7. Pretty Woman
8. Citizen Kane
9. Trollflöjten (The Magic Flute, 1975), Bergman and Mozart
10. Ba wang bie ji (Farewell to my concubine, 1993), if Chinese opera also counts.
11. Hsi yen (The Wedding Banquet, 1993), Wei Tung's date from the marriage agency is an opera singer, who demonstrates her skill.
12. Mademoiselle Else (2002), the opera in Vienna is featured.
13. Hans Christian Andersen: My Life as a Fairy Tale (2001), the opera in Copenhagen (if I remember well).
14. E la nave va (1983), brilliant Fellini with diva's competing with each other and the machinery of a luxury ocean liner!
15. The Great Caruso (Mario Lanza)
16. Dangerous Liasons
17. The Untouchables
18. The Fifth Element
19. Victor/Victoria
20. The Unsinkable Molly Brown
21. Interrupted Melody
22. Camille
23. M. Butterfly
24. Going My Way (Rise Stevens in scene from Carmen)
25. Madam Bovary
26. Original Sin
27. 27. Farinelli Il Castrato (1994)
28. Topsy-Turvy (if Gilbert & Sullivan counts) Sure, the more the merrier
29. The Bride Wore Black (Jeanne Moreau meets one of her intended victims at the opera)
30. Love and Death (if he was at the opera, OK)
31.. The Awful Truth (Irene Dunn sings an opera for a small audience while Cary Grant falls out of a chair and creates a ruckus in the back of the room)