Okay, three answers:
- Does [this](
http://upload.wikimedia.org/wikipedia/commons/e/ef/Belgique-Communes589-Provinces10.gif) help?
- Otherwise, in the right margin on [this page](
http://nl.wikipedia.org/wiki/Lijst_van_Belgische_gemeenten_naar_bestuurlijke_indeling) you can get maps for smaller sections of Belgium. It at least looks like they'd line up properly...?
- The map you're using for the Netherlands seems to be "own work", so I put in a request with the author, asking if he could also upload the map for Belgium (if he has it of course). I'll let you know if/when he responds.