I don't know if you already have, but perhaps contacting Forest River may help. On our previous trailer, a Holiday Rambler Alumascape, both of mine were damaged due to tire malfunctions. Even though the trailer was 6 years old and the styling had changed, HR had leftover stock they sold me at a great price. Couldn't hurt to try FR.
I did search prior to calling HR, and found a number of stores and parts houses that sell replacements. Some are a very close match to the factory sets on various brands/models:
rv fender - Google Search