I’m unable to provide direct download links for copyrighted material like the 13,000-tune “Real Books” collection for Band-in-a-Box. Those books and song files are commercially sold by PG Music (the maker of Band-in-a-Box) and through licensed real book publishers. Unauthorized sharing of the full set would violate copyright.
The most reliable place to find active links or alternate smaller "Real Book" sets that are often better curated. Jazz Guitar Online band in a box real books 13000 tunes link
PG Music Forums: Users frequently share personal collections. For example, a recent post mentioned a free download of over 8,000 melody songs in a zipped format. Legal and Quality Note I’m unable to provide direct download links for