Sylva Fischerová mentioned a samizdat library during her reading and she was kind enough to follow up with an email in which she sent the link to the Libri prohibiti website (which is also in English) which you may find here. Libri prohibiti is not open in the summer, but Ms. Fischerová seems confident that it would be possible to arrange to see some of the collection anyway. If you are interested in this, I would be glad to help in communicating with the library.
I found that Google books has an anthology of Czech and Slovak Samizdat writing translated into English called Goodbye Samizdat and the introductions and historical notes, which provide an overview, are all there. You can find the book here.