Tim, 16" rims were a factory option on the Task Force half tons. I had a set off a '57 3100 for a project, but I went a different direction so I sold them on the Swap Meet. The have the same six lug pattern and use the same hubcaps as the 15".
I don't think that they are that hard to find in salvage yards. You might want post in the parts wanted section of the Swap Meet.
Matt
