First thought is that a competent body shop can repair most damaged doors, though the labor won't be cheap. But if you can't find a replacement, you do what you have to do.
Second is that the doors are typically a skin over a frame, and a local metal or fiberglass (whichever it is) fabrication shop can make a new skin and straighten the frame. Or make one if need be. Shops that do RV repairs usually have a "goto" fabricator who can do that. Mike's RV Collision in Wilmington, NC, got one made for my coach as part of a larger repair job..
Third is that there are sources online for many shapes and sizes and you might get lucky. Here's a few: