As far as breast forms go, I'll admit, I have little experience as I bought two pairs, not quite as big as you gals are talking about, however, I quickly moved into breast chest plates as I wanted to have cleavage for others to admire while I'm around them. I'm currently wearing one that gives me size 32G breasts and the chestplate comes with pre-filled solid silicone breasts. There are two sites that I'm aware of that carry these:
www.Feminization.us and
www.aliexpress.com
Aliexpress is from overseas, but cheaper (even with shipping) and I haven't had any problems working with them
Feminization seems to be US based, but some of their text and language choices makes me think otherwise, however they have more options than the other site, but are more expensive for the same product.
You could also try Amazon.com as they also have a large selection of breast forms, but they don't have any high quality chest plates or silicone leggings like the other two.
P.S. I too cannot wait for the USA get caught up on the Transgender accessories and clothes so that capitalism can start to drive the prices down.