Ryan, It is possible that Mobility RV might have the bumper ends. I doubt it, but it is possible, they get all of Winnebago's obsolete parts and I have found quite a few things there. The age is against you but if the same ones were used for several years it is possible. You can Google Winnebago parts or Mobility RV and find their website.
Back years ago we had a 1976 17.5' Mobile Traveler and sold it for $6500 and turned around and bought a 1973 Mini Winnie for $2500. I opened the door and gutted it, threw everything out the door and rebuilt the whole interior. We drove it on many trips out west, the longest being from Ia. to Los Angeles Ca. We loved that old thing and sold it to our son. He used it for several years and sold it to a friend, last I knew it was still in existence but failing. lol
I have been a Winnebago lover ever since, they have a great roof and good construction.