I am pretty sure I have the one you are asking for on the boat as a spare. My 50 amp to twin 30's had one prong overheat about two weeks ago and damaged a socket. I got a new 30 amp cord and eliminated the Y at our home slip. I will need to replace it for future traveling.
Having said all of that, if your splitter is in good condition and you are interested- I would send you the one you want and pay you fair money for The difference on your splitter. I need a 50 amp 125/250 volt male to twin 30 amp female. Please PM if you are interested