There are no legoshops in the Netherlands. There are just normal toyshops in Maastricht with normally no exclusives.
The only thing I can advise you is a Top 1 Toys shop in Vaals, around 20 Km to the east and almost to Aken/Aachen. Because it has almost all normal sets with very low prizes.
For Example: A Star wars Battle pack would cost last year at a Intertoys or Bart Smit shop 15 or 16 euro, But I was there on holiday and the sold the same battlepacks for just 10 euro.
(This is not in all Top 1 toys shops)
I was also in a german toystore in Aachen called "Teddy and Co"and it had a little pick-a -brick wall with little yellow plastic bags which you could fill and take it away for around 5 euro. It were not very special bricks but it was nice.