I found some?
From The Lost Media Wiki
I found a youtube video of chowder bumpers. Pretty sure they're legit, but I don't know "which ones" I found. https://www.youtube.com/watch?v=KS2rsiQIYuo
Here are a bunch of "up next" bumpers, but many aren't listed so I don't know if they're legit (I've been fooled by some before). https://www.youtube.com/watch?v=GiOTERk57NY
Here's one that based on the age of the video and remembering the bumpers, have many real ones, but again, not sure which to categorize. https://www.youtube.com/watch?v=LtiIHW9gdI8