I have used most of these sites (haven't made the infinity dress):
http://craftstew.com/sewing/free-skirt-patterns
http://www.angelfire.com/planet/mcshelpsite/sewingstuff/freepatterns.html/#adult
http://rowena.typepad.com/rostitchery/infinity-dress.html
http://www.allfreecrafts.com/sewing/index.shtml
http://www.simplicity.com/t-free-projects.aspx
http://www.theribbonretreat.com/custom/free_projects.aspx
http://craftstew.com/sewing/free-skirt-patterns
http://rowena.typepad.com/rostitchery/infinity-dress.html
http://www.angelfire.com/planet/mcshelpsite/sewingstuff/freepatterns.html/#adult
http://www.allfreecrafts.com/sewing/index.shtml
http://www.simplicity.com/t-free-projects.aspx
http://www.theribbonretreat.com/custom/free_projects.aspx