Seattle is on your info.....
Just my opinion...
Call Allied body in South park, see if you can send pic and see what they say.
(Years ago I built a camper and they were able to get smaller "corner caps")
Heiser on Tukwila or Intl blvd (or what ever they call the street now) across the street from old Boeing headquarters (the old drive in before Boeing took it over)
Western trailer repair near airport and Lucille st ?
Allied body was more helpful when I was gathering parts, for me anyways.
And there is guy in south park (proper) that does crazy custom stuff, and charges crazy also:)
Hard to match up sometimes if ordering online, but maybe this will help.
https://www.google.com/search?q=trailer+corner+caps&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjgyYb4rN3gAhWI4FQKHTFWDvoQ_AUIDygC&biw=1366&bih=623