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