Bell Housing Inspection Cover? Local auto wrecker would be a good place to start. I'd suggest you get a positive I.D. on just what transmission is in the vehicle first. That should help narrow the search for the guys at the wrecking yards. If the trannny is a common unit a new cover may be available from the dealer...most likely at the premium price. If you visit the dealer with your VIN they should/might be able to nail down the tranny type and help with a parts search perhaps. Heck...maybe a transmission shop has got an old one you could cannibalize for the cover.
T.