Most places try and pass off "chubby" chicks or ones with big tits as BBWs.
You can get some from these places
http://www.tm-photo.net/ (also some sold thru ounique)
http://www.ounique.com/
http://www.adultstockphotos.com/ - couple sets
http://www.adultimagebrokers.com/ - 5 sets
http://www.web-legal.com/xtitles/
Good luck...