Without a doubt, the largest tomato database on the web is Tatiana's.
She lists almost every known OP heirloom tomato, along with sources to get seeds for most of them.
She offers many of them herself...by far the largest supplier of Russian/USSR varieties.
She is based in British Columbia (just north of Vancouver), and is great to work with.
http://t.tatianastomatobase.com/wiki/Main_Page