Most Generator stores and larger RV stores have the needed adapter
Any electrician or electrical shop can make one.
You can as well if you know what the Bleep you are doing
NOTE.. You may need to do somethign "illegal" if you have a hard wired surge guard in your RV.. and you should have one (One of the top end ones that monitor voltage and turn you off if it's not right)(
That something is connect green and white together to teh white screw on the generator end of the adapter . Green is often Not Connected in the Generator,