Look for a farmers market. You can also try growing them.
http://www.rareseeds.com/store/vegetables/tomatoes/
http://www.seedsavers.org/category/tomato
Burpee, Jung, Territorial Seeds, etc.
http://t.tatianastomatobase.com:88/wiki/Category:Tomato_Variety_List
Good hunting, good luck, good growing!
(Then distant thunder is no longer distant! Getting off the computer!)
BFLR