Just Google for breat photos using the image option, you'll probably find 40 million pairs!  As far as copyrighted breasts go, if you're outlining them in Photoshop, what woman is going to contact you screaming, "Those are my breasts! You stole my copyrighted breasts!"

Usenet is nothing but breasts, billions of them.  Go look there.  Or go to the 7-11 and buy a smut book.

I would think drawing a breast wouldn't be complicated...ugly, old, young, BBW or otherwise.  Or as suggested, use your imagination.