I did some research and discovered that red walnuts are a fairly recent creation. They are not genetically modified and were created using natural methods of grafting Persian red-skinned walnuts onto larger and creamier English walnuts. There are currently two varieties of red walnuts; Livermore and Yolo Red. Both were developed at the University of California at Davis in the late nineties, and it's only been in the last two to three years that the trees produced crops. The nuts are larger and the shells are a little harder than other walnut varieties, and the trees grow slower. To retain their red color, they should be hand-shelled; machine shelling causes the red layer to dull and chip off. Since there are limited amounts of producing trees, these walnuts are currently only found in high-end stores, some farmer's markets, and online. Their high price is due to their rareness.
Red walnuts are late-producing, so they are available at the end of fall and in the winter. E.G. right now!
Don't have access to a California farmer's market? Haag Farm in Central California grows Yolo Red walnuts, and during their limited season will sell them via their website. Click on "Catalog Orders" and select "Yolo Red Walnuts" in the drop-down menu.
(Image: Kathryn Hill)