I was able to find the elusive lower fridge
vent for my Trillium
4500, the Dometic VT-24-1.
WKS Tent Trailer Rebuilder
Wes rebuilds tent trailers in or near Edmonton AB. Many of the parts used in those are what we have in our eggs. He has some used parts on site. Check out his web site to get an idea of the types of things he has.
Once I was able to connect with him, he got back to me within a day saying he had the part. That was Saturday, by Tuesday I had the vent.
Payment by credit card over the phone. Shipping details by email.
You might want to add him to your favourites, I have.