Find a local foods chef or baker, if you know of any in your area. Also, contact one of your local CSA farms. They will often sell for you or know of some local folks who would be interested in them. My friend brought her extra duck eggs to her CSA on pick up days & left them for the others. She had to buy 4 new ladies this year because now she has a huge list of customers that come to her for duck eggs.
I don't know what the deal is with people & duck eggs. I don't love them for scrambled eggs or in my potato salad, but they make the most incredible custards, cakes, etc. If it doesn't have a commercial, jingle, or cooler section at the grocery store, it can't be good.
I also think the idea of giving a few with your chicken eggs is a good one. My SO was dubious about ducks, at best. When I picked up my Anconas I also got a dozen duck eggs from the breeder. I promptly made brioche and a loaf of my "monkey bread" (banana chocolate chip & peanut butter bread) with them & he is sold now.