You can get a sizing kit from Allergan but in no way do the implants feel natural. They are basically small bags filled with water.
Breast implants are regulated medical devices and as such the FDA will only allow them to be sold to physicians for implantation. Most plastic surgeon offices will have implants for display but few will let them out the door with a patient. They are hard to come by for display.Natrelle sells a kit of 4 water bags in different sizes along with a bra with pockets. I've had one patient use the kit and it seems more confusing than anything else. I was lead to believe it contained defective implants that could not be sold but the water bags are a pretty poor substitute and the bra is pretty flimsy. You would do just as well to go buy your own bra and use zip lock bags and water or stockings and rice to make your own "implant."