Duck fat recently cropped up on the shelf of my closest mainstream grocer, shelf stable, I think it was a 12 oz jar. Surprised to see it there. I think it was near the cooking oils, shortening area. Don't recall the price nor the brand. Looking online, Rougie and Delice look like the primary brands.
Prior to that I had only seen it in specialty butchers.
It used to be available in 12 or 16 ounce jars, don't remember, at the Kroger affiliate down the street. On the shelf with coconut oil, avocado oil, etc. Then I went to buy some and gee, no longer on the shelf. Oh well.