The best I've found so far is:
http://www.marko.com/basic.html#blue or
http://www.marko.com/basic.html#navy and this is the main page of that site:
http://www.marko.com/index.htm They also have a few e-coupons if you scroll down on the left-hand side of the page....
They have a nice variety in the size of the checks and such...
As for the fabric for your curtains, try:
http://www.fabricsunlimited.net/gingham.html