My former dealer (for my former Bighorn /
https://www.bamarv.com/) likely has one.
Long after purchase I noticed that half of my vents were "blowers" while the other half were "returns". The returns had a separate twist-locking ring inside that held a filter in place, and I was missing ONE inner ring and filter. It took awhile but they eventually procured one for me (I believe direct from Heartland / their generic sources weren't the same size). Anyways, as I didn't need the entire vent I told them to keep it in a junk pile as it may come in handy. I believe it came in two colors (ivory & white?), I don't know which one I received.
Give them a call.
I'm now in a Tiffin Phaeton.