Volunteer as a OB RN in Miami

I'm trying to find a place in Miami where I can get some experience as an OB nurse. I am a child birth educator and my passion lies in this area. However, I always get denied a job for lack of experience in the field. I am already an Interventional Radiology RN, I've been for a few years now, just no OB experience. I am willing to volunteer, just don't know where. Can anybody help, please?! Maybe some input on what I should do.