Uh-oh...
My theology forbids me to believe that there remains undiscovered scripture in the world.
However, for the same reason I'd like unrestriced access to the Vatican Library and a staff of interpreters, I'd be interested in reading (for notional example) a letter from Luke the Physician to Paul asking how his "thorn in the flesh" was doing, and perhaps naming it (shortness of vision? a poorly healed fracture from being stoned?); or a letter from some otherwise unknown Judean finshmonger to another about how he hadn't seen Simon the Fisherman for years and then saw him preaching on a streetcorner under the name of Simon "the Rock", and how it all seemed to make some sort of sense.
Bests!
Are you serious?