Because KLM announced to stop in-flight sales I think they will get rid of all items.
I have seen disappearing trolleys and beauty-cases in the last few months while they launched just few weeks ago a limited-edition of trousers (well advertised via Instagram with fashion bloggers).
Anyway some memorabilia can still be found on airport shops (air-side but also landside) while, if you really look for something rare you may ask to a specialised shop which is just 10mn by car from Schipol. Its name is Aviation Megastore and they have a website which I dont know if I can advertise here. Eventually look for it and write them before you go there. They can keep reserved goods for free until pickup . You can do the same with airport shops but only if you return to Schipol. Alternatively the best is the free delivery on board...obviously if the item is still available on shop.klm.com