The outward correspondence of the Governor of WA between 1851 and 1868 can be viewed on 5 microfilms stored in the SROWA microfilm cabinet on level 3 of the State Library of WA. A couple named Buchanan have indexed these volumnes. You can find these indexes in files stored in a cupboard on the left hand side of the door to the SROWA Research Room. Look for the Name Index in the file(s) that reference your convict. You will then know which letter number(s) to look for on the microfilm.
The first three index files are available to download.