Depending on the individual variety, sometimes images can be located by googling the S number, but unless this is a one-time need, I respectfully suggest buying the book/books/pdf.
I have the 1857-1909 Snow books as PDF--but I shouldn't be sharing them. But there's an online listing of Snow varieties (and others without Snow #s) at this site. It's under construction, but there are a lot of photos up already. Indianvarieties.com
go here: http://indiancent.wikispaces.com, and follow the links, you can find some pictures and pricing information