Use whatever confectioner's sugar (or icing sugar) you can find. It will most likely be 10X but occasionally you can find 4X. We are unaware of any other sizes being available to the consumer market in this country.

We have also not come across any recipes in recent memory where the size difference between the grains of 4X and 10X sugar would make any discernible difference.

If one of your dinner guests impulsively blurts out, "Oh my gosh, is this 4X sugar?" after biting into your fabulous dessert, cock one eyebrow, smile mysteriously, and ask, "does it taste like 4X to you?"

No one needs to know what size sugar you're using.