Since the Ram 50 wasn't made in very large numbers, you might check its Mitsubishi twin for parts availability. The Mitsubishi was the Mighty Max.
I just checked Rockauto for you on both and the tailights that came up for the Ram 50 looked like those off of an 80s Dakota, which I know is not right. Nothing came up for the Mighty Max, so you might end up having to scour eBay.