What is the plural for the Book of Mormon?

Consider saying "copies of Book of Mormon" instead.

With such ambiguity, changing the sentence structure would be wise. I would say “copies of the Book of Mormon”.

Copies of the Book of Mormon. People generally avoid saying it in the plural, though, so I'll usually hear people say "would you like a Book of Mormon?" or "everyone get out their Book of Mormon". Sometimes, when it is necessary to talk about it in the plural, people slip up and say "Book of Mormons". But I've never heard anyone say "books of Mormon". "Copies of the Book of Mormon" is the correct way, even though people say it wrong sometimes. In the end it's not a big deal, people know what you're talking about.