This one might be worth a visit. http://www.lpsportwapens.nl/
Not in Amsterdam but not to far away (Kenauweg 32, 2331 BB, Leiden) and aimed at airguns.
As mentioned above Airguns.nl or better known as Joppies Dump is also a nice shop but specialized in building the really high power Beaumont airguns, like 100 fpe plus and 8mm or bigger caliber. Not much to do with 16J there. But sure worth a visit. It is a combination of an army dump shop on the ground floor and airguns on the 2nd floor.
I do not personally know any gunshop in Amsterdam but there are some. Look under "Noord Holland" here: http://wapenhandel.info/web/?page_id=75
But these will be mainly firearms orientated.
A big one for airguns is www.krale-schietsport.nl
. But quite a travel from Amsterdam in Staphorst, province of Overijssel.
Have a good time in The Netherlands Burjaka, and remember that not the whole of the Netherlands is the same as Amsterdam. A'dam is just a big city crowded, full with tourists and the big mouthed people trying to empty these tourists purses
like in all big cities around the world.