I've seen small/medium fake breasts in JAV, like Tsubasa Amami, Kaori Maeda. Even small fake breasts are not very convincing. I think fake breasts are not as common in JAV is people here seem to think.
Sora Shiina seems very natural to me, both her face and body, for better and worse.
For some reason, I always thought Ayu Sakurai has fake breasts. I don't remember why. Maybe I confused her with a different actress, or maybe I am just an idiot.
Yes of course some girls have fake small breasts. Maybe Akiho Yoshizawa is the name you are looking for ?