Stofftrucke has a pretty large selection (for Zurich standards) of all types of fabrics. You can take the #2 tram to Sihlstrasse and you'll see it right across the street. (It's on the second floor. When you walk in the front door at ground level it looks like you're walking into a shop just of football jerseys.)
If you don't find what you're looking for you can always go to Manor for curtain fabric -- you can find the fabric selection on same floor as the kitchenware.