I'm pretty sure fabric.com has the cotton or bamboo w/lycra blends you're looking for. As far as the elastic goes, I was reading Verypurpleperson (Novita's blog) the other day and she discussed the kind of soft, dyed elastic that you're probably looking for. She lives outside of the U.S., so might not name any sources for buying, but you could find out the name of the elastic that way. Good luck!
Nancey
http://mykindofanonymousblog.blogspot.com/