You won't find the adapter you're looking for. A straight or L-shape ground pin indicates a NEMA 10-30R 120/240 volt socket.
The only available adapters convert the 50 amp socket to the 120 volt only NEMA TT-30 outlet, which is identical to the 10-30R except it's 120 volt only.
Don't try to mix and match the two. Although they're physically identical except for the shape of the ground pin, the 10-30R has two hot leads and a combined ground and neutral. The TT-30 has a single hot 120 volt line, a neutral and a ground.
Many people have inadvertantly applied 240 volts to their 120 volt 30 amp RV plug by ignoring the differences between the plugs.
50 amp RVs do use 120/240 volts, but it's with a separate full size neutral and ground. Before you make your own adapter, be sure the 10-30R socket has a full neutral, not just a ground connection.