I always bought the Z hats at the dealer when I got my oil changed but they no longer have them =(. Anyway I was looking for an alternative place to buy them. I unfortunately did not find the blue one that I was getting before but I was able to find some similar ones that looked nice as well as some shirts/jackets and other stuff (ordered two of the jackets and a polo shirt as well) from:
Nissan Online Company Store
(in the shop by Program -Z section).
Had some interesting stuff on there so I thought I would share.