Fashion Modeling Agencies: The proper way of contacting them?

I'am inspiring Fashion Photographer who has a very BIG interest of photographing models. Trying to contact Agencies is like trying to get your hand out of a lion's mouth. I'am not a newbi to photography but i have 0 experience in fashion. I feel as though mastering key elements in "photography" itself will kinda contact to my fashion side as well. So how do i go about working with agencies to possibly build a great portfolio for myself?