One of the mysteries about Orson Welles' Merchant of Venice is why it isn't better known. But that's only one mystery among many.
I learned of the film's existence when skimming through the bonus disc on the Criterion release of F for Fake; it contains a documentary about the many incomplete projects Welles left behind during his long and (usually) illustrious career. Welles apparantly actually completed all the filming for his version of Merchant of Venice—but then some of the rolls of film were stolen, and the production could not be completed.
The documentary provides about seven minutes of the very rare footage as well as a recording of Welles delivering Shylock's most famous speech, made some time after shooting stopped on the film. I've extracted part of the film version of Merchant of Venice and the entirety of Welles' delivery of the "Hath not a Jew" speech. May those who took the footage immediately repent and turn it over to the nearest authority. The world needs the rest of this Merchant!
Links: F for Fake at IMDB. Orson Welles: One-Man Band at IMDB.