My two cents worth
Golden Syrup--light treacle, a syrup from sugar cane or beets. Sub light corn syrup with a tsp. of molasses
Double Cream--there is no sub and you cannot buy this in the states, unless you have a cow or a share in a cow. It is the thick, unpasteurized, cream that floats to the top of the milk. Whipping cream is like skim milk compared to double cream and is an American shame.
Corn Flour--Corn Starch
Tapioca Maltodextrin--tapioca starch. Very similar to tapioca flour which can be subbed if you can't find the starch. You would just need to use a little more. Indian groceries usually carry the Tapioca Malto