Tranny/Motor spacer plate

The guy I got the car from neglected to put the spacer plate in when he rebuilt and installed the motor! Is there a way to shim the starter? If so does anyone know the thickness? (I would really like to fix this issue, but cannot find that plate anywhere around here, and I have to drive for an hour to replace my starter (under warrenty) when it kills the starter) Any help would be great!!!!!!!