There is a whole board for discussions of progesterone and the topics are mostly about the creams. You can find that by clicking here for the Progesterone Board.
In the US, at least, no prescription is needed. It's sold at health food stores and in women's catalogs. You need to be careful, though, to get a good quality - not a "whild yam" cream.
Dearest has provided a wonderful area with all kinds of info for us called Educate Your Body. There's an important article in there called Progesterone and Women's Health which would be informative and helpful reading