What's the US equivalent of double and single cream?
In the UK, single cream is a milk product with at least 18% butterfat.  Double cream has 48% butterfat.  Neither are common in the US.

If you can find clotted cream, which is 55% fat, then there is a chance of making double cream at home by diluting it.  As some clotted creams have a cooked taste, there may be other solutions.