I have never seen one like that but do have a suggestion for you. In fact two of them, one for now one later
A company called Coil-%-Wrap (As best I recall) makes something called a plug dog.. this is a nylon (I think) webbing thing that you put one end of it over your 50 amp plug, then you "Wrap" it around the plug head and put the other end over the pins.. Now you plug in, and when it comes time to unplug grab the handle thus formed and pull.. Works great.
Recommendation two.... When you eventually need to replace said plug.. Check out the Camco Power pull.. Now I've heard complaints about that one but the one I have is a competitor's same design,, Works great.(Wish I could recall the name of the competitor)