So unfortunately I've tried all avenues at this point. I called Merch Guest Services and while super nice, they said their supervisor said they could not issue a replacement part, even for sale.
The @WDWGuestServices Twitter account never replied to me and looks like it hasn't been updated in months.
Lost & Found closed my case, stating they couldn't find it, despite the guy on the phone at Lost & Found saying cases stayed open indefinitely. He said maybe try Guest Services again in a couple of months to see if I get someone who'll give me a different answer.
It'll be a long while before we return to WDW, so my last resort is to try and DIY a replacement part and hopefully I can make it fit better than the original anyway.
Thanks for the attempt to help, though! I appreciate the responses.