I got same problem as you do
I'm building an extremly (to the edge af fanatisme) Sigmarite themed Ostland army based around the Knights of Sigmar's righteous fury, an templar order I invented myself and for my knights on foot (or great-hammerers) I recently bought the greatswords box and
received some Chaos hammers from a friend. I still have to begin construction though.
Off course if you want koww you would be better off with the knightly order box and a greatswords box since that way you also get the iconography of koww
Alternativly you could buy some Teutogen Guard, they were released by GW for the Storm of Chaos Campaign and represent knights from Middenheim. A quick google search will reveal what I mean. unfortunatly they are very rare!
Whatever you do, please keep us updated in the miniatures section, i'm extremly interested in your progress for obvious reasons!