I belong to a few different fabric co-op groups.
Some will run organics from time to time, but it's rarer than other fabrics.
Here are my favs:
All Natural Fabrics (Michelle is FABULOUS and ships really quickly - some coop groups can be kinda slow)http://groups.yahoo.com/group/allnaturalfabrics/
chloefabrics (haven't actually ordered through this one yet - waiting for my fabric budget to increase
It has great patterns that I hope to buy for DD's clothing)http://groups.yahoo.com/group/chloefabrics/
This-End-Up (again, I haven't ordered yet, but became a member to be able to purchase fabrics & notions for sewing diapers)http://groups.yahoo.com/group/This-End-Up/