Richard, Welcome to the Stovebolt. If you haven't already, feel free to go to the Welcome Forum and introduce yourself. Tell us a little bit about your projects there.
If the handle is the same as the 47-53 version, no suppliers that I know of, offer that part. However, if you place a wanted ad in the "Truck Parts Wanted" forum in the Swap Meet
section, someone might be able to offer you the part you need. Another option is to follow one of this site's Tech Tip and make your own from a front door handle. Modifying a 1947-1951 (Advance Design) front door handle for use as a rear barn door handle
That is, IF it is the same as a 47-53 version.