"san Marzano" appears to be (from my reading) a "class" of tomato - using various varieties - I know that there is an heirloom open pollinated variety of paste tomato by that name - but several articles on the web mention various named varieties of "San Marzano's" and several more mention the secrecy in which producers are keeping their hybrid seeds.

You would probably do better to research an open-pollinted heirloom paste tomato specialized for your own region.