The serial number O-5083 confirms you have a
1956 30' Sovereign of the Road built in Ohio.
Used Airstream doors do show up for sale occasionally, but you need to be diligent about searching various Airstream related websites and Facebook pages, of which there are many. A door from a different year might fit or might not fit. You'd want a door from close to
1955 as the further away in either direction the door dimensions and styles definitely changed.
Airstream doors varied with some opening in either direction (left or right), often in the same year. Looks like your trailer originally had a door that opened "left" (i.e. the hinges were on the left (rear) side of the door when facing it from the outside. This allowed the door to open all the way when the windows ahead of it were open without crashing into them. Doors opening in this direction are often referred to as a "suicide" doors. A door that opened the opposite way might be able to be fitted to your trailer, but would create the potential crash condition with the windows.
Good Luck!