I use these, they didn't do the blue when I bought them so mine are all black. 100% cotton, heavy fabric and really durable. Nice and warm too in the winter, best overalls I've ever worn.
http://www.lbrador.com/en/Products.php?load&node=465340&parent=622908#
http://www.lbrador.com/en/Products.php?load&node=465340&parent=622908#