If there are no reports or even hints amongst U.K. and the rest of Europe's retailers that the paper in question has been discontinued by Foma but two large retailers in the U.S. will no longer stock it then there has to be reasons we are not being told about.
It makes absolutely no sense for Foma to discontinue a product in a large market such as the U.S. So what's changed?
Just because we buy the stuff here, doesn't mean that it sells as well on the other side of the pond and the US retailers may well see a lower number of stock-items as being easier to sell. At some point the volume discount on any group of products will be reduced so it could also be a volume/minimum-quantity/pricing thing. In a retail environment there is frequently more to consider than "available - yes or no".