I found at least three Brazilian sites that could perhaps serve as providers: http://bondfaro.com./ and
http://buscape.com.br./ -- both accept ISBNs in their URLs.

That is, I assume you pass ISBNs in the URLs then does some form of screen scraping.  If not, some other sites may be
willing to serve as providers with some form of API, such as http://livrariacultura.com.br./ or http://cbl.com.br./
which actually links to http://xpress.superpedido.com.br./testes/cbl/.

Is there documentation on the method, or is the source code the documentation?  If you need them, here are some sample
Brazilian ISBNs to use: 8521000324
8731103479
85-213-0929-5

Date: 2008-11-12 02:14
Sender: Carlos Costa

I propose not using (only) commercial websites. The link
is cumbersome, but at

http://www.bn.br/portal/index.jsp?plugin=Isbn&url=/site/pages
/servicosProfissionais/agenciaISBN/isbnBusca/FbnBuscaISBNCatalogo
.asp?pField=ISBN&pIntPagina=1&tit=Procura%20por%20ISBN&am
p;nu_padrao_apresentacao=26

one can perform an ISBN search for any book published in Brazil.
This takes care of a lot of technical books not found in most
commercial websites (with the exception maybe of livrariacultura.com).
The website above is from the actual government agency which
regulates ISBN affairs in Brazil. I think this approach should
be followed for other countries. The only drawback being they
don't offer images.