May a rabid opera fan weigh in here?
If you're looking for music from an opera called "Ludvik" in connection with "I Never Saw Another Butterfly," I'm afraid that you're barking up the wrong tree.
The children's opera that was performed at Terezín was actually titled "Brundibár." It was composed by Hans Krása. For purposes of the play, Celeste Raspanti changed the opera's title and fictionalized its plot summary - I suspect (but don't know) in order to avoid any possible copyright infringement.
The opera is published by Boosey & Hawkes, which also licenses performances. Their piano-vocal score, which I bought some years ago, has the original Czech text and a creaky English translation. Tony Kushner has created a new English translation, but I don't know whether Boosey authorizes its use, or if it has to be licensed separately from the music.
There are several complete recordings of the opera. Most online retailers of classical music should have them. Amazon lists a number of them, including the one that I own, which is from the Channel Classics label. That one has the advantage of being sung by children, as the composer intended. Some of the other recordings use adult singers; to my ears, that just sounds wrong, and is nowhere near as poignant. As always, if you plan to use any of these recordings in your production, be sure that you have the proper legal clearance to do so.
The Hérold and Chopin pieces mentioned earlier in this discussion relate to an opera whose title simply happens by coincidence to sound similar to the title that Raspanti used; they have no connection that I know of to the camp or to the play.
I have long dreamed of staging a double bill of the one-act version of "Butterfly" and an English rendition of "Brundibár." I think that would put the opera in an understandable (and moving) context for contemporary audiences.
Hope this helps!
-------------------------------------------
Jeff Grove
Theatre Teacher, Aesthetics Department Chair
Stanton College Preparatory School
Jacksonville FL