ABE Books. A librarian told me about it, and it's wonderful. OK, so I have yet to refine my search words to narrow it to Austria early 1800s, but I haven't played with it much this morning. Booksellers from across the world have listings here, with basically the same ratings as Ebay, but all books and nothing but books.
I intend to take my time with this site, you never know what's going to pop up!