and of course, eBay. There's a seller on there, called the TomatoSeedLady that sells almost 25,000 seeds for 109.45 & they're all heirloom. She also has over 100 types of heirloom tomatoes available.. You can buy a packet of mixed tomato seeds (500 or 1000) for around 5.00.
(Hope this post doesn't get deleted, as it contains many links... But I think it's relevant.. And I didn't see any seeds in Alissa's shop, otherwise I wouldn't have posted this.)