I can't keep any duck eggs in the fridge here! I live in rural IA, but not far from a university city and I have a few regular Asian customers now. They tell me duck eggs are what they grew up on and they have a hard time finding them here. Also, Asian grocery stores. I've had a ton of luck on Facebook marketplace, but be aware, their autobots will flag it at first because it thinks you're selling an animal. Just say that you're selling eggs to eat and then it's no problem afterwards. Aas others have mentioned, Craigslist too. Of course now everybody is molting so not as many eggs after I built up all these customers.