as I am aware from my own and others' practice, the BIORAD Mouse anti-progesterone monoclonal antibody, clone 1188/344 would fill well to your request. It is specific for progesterone. The mouse anti-progesterone exhibited the following cross-reactivities in ELISA: Progesterone-3-BSA:100%; Progesterone-11-BSA:50%.
sometimes the best antibody against a small target, is the receptor itself. If targeting progesterone, do you think the PR will do in lieu of an antibody? Can you test it side by side with the aforementioned antibody? (PG Ab suggested by Ilya B. Tsyrlov )