FWIW, I live in Amsterdam and from experience I can say it's not the
easiest place to buy new Pentax gear. Even the "official Pentax
specialist", a shop named Esser, generally has little in stock and sells at
or near the importer's recommended retail price. For new gear, I concur
with others who have recommended kamera-express.nl. There are a few nice
second-hand places that you might want to visit though, most notably in the
Haarlemmerstraat just west of Central Station. The city of Utrecht (less
than half an hour from Amsterdam by car or train) has some excellent shops
as well.
I don't know where you're located, but I'm under the impression photo gear
tends to be a lot more expensive in Europe than in North America. Not just
photo gear, FTM... when it comes to musical instruments, we usually pay
around double the US prices (even when the instruments are manufactured here).
Zed