The Rampjaar blog is probably the best place to start for William's Dutch army:
http://rampjaar.blogspot.fr/The League of Augsburg's forum ('fighting talk') occasionally has the odd discussion on the subject of Dutch troops as well.
Clarence Harrison is in the process of making a whole slew of Nine Years War flags. There are two sheets of Dutch standards among them, though they would not necessarily be correct for the 1670's (the Foot Guards below are definitely post 1688, for instance) :
http://www.northstarfigures.com/list.php?man=101&page=1You may also try to talk Iain at Flags of War into making some flags for the Dutch War.