That means either that don't buy it from the distributor, or the U.S. distributor no longer imports it, and they don't have any grey stock. I picked up fresh 160NS in 120 when I went to Singapore for quite cheap. You can get it online too.
160NS is a current product, 400X isn't
^-- all pro colour neg
160NC only in 4x5, no quick loads, etc..
160NS is more formats.
According to their site, they tend to announce discontinuations on there.