You can get it by mail order, but a recent trip to various expat Brit outlets in New York yielded what was to me more like a somewhat velvety creamcheesespread than the soupier, clottier Double Devonshire clotted cream of memory.
The first book featured family standards like Zippy Olive Beef Spread, made by combining whatever wine is on hand, instant minced onions, creamcheese, mayonnaise, chopped cocktail olives and beef cut up with kitchen shears.