Silicones come from Smoothon dot com, and Plastics from polytek dot com.
To start, you could try the same method i did with the witchblade parts, but use laytex. So you can get that from the art store.
Coat half the baby(plastic luke or leia, not rose
) with laytex rubber. Then fill the mold box half way with laytex and then place the baby in it.
This way the laytex will get into all the crevases and then when you place it into the mold box in the other rubber, you wont need to worry about air bubbles.
THis is how i do my coins.