They list every species of seed they've ever carried, but they seldom have more than about half of the listed species in stock. It's hard for them to source quality seeds, and they can't risk buying significantly more than they can sell, since seeds are perishable, and they need to turn a profit.
That said, when I looked earlier today, there were quite a few species in stock. Just search "Quercus" to get a list of everything they have.