Do you need a market other than Sittard, Eygelshoven or Heerlen? I’ve found a database that lists all of the markets across the Netherlands, to include specialty markets of cheese, books, or antiques.
The home page has a description of Dutch markets, but the real lifesaver is the search engine. You can search by municipal region (Brunssum, Heerlen, Landgraaf, Kerkrade and Sittard-Geleen are examples) or by day of the week. The entries will include specific location of each market and it’s opening hours.
Search to your hearts content, you might even learn something new about your usual stomping grounds. Example: They list an organic market in Sittard on Steenweg which takes place on Saturdays 1000-1700.