I found by accident the website of the Centro de Estudios de Historia de Mexico Carso, owned by Carlos Slim, and it has a large colection of digitized documents and photographs. I'm still browsing through the website, but I have seen there are some collections about Nueva Galicia and the war of independence. The site is:
http://www.cehm.com.mx/Es/archivo_digital/Paginas/Consulta_de_archivos_…
Digitized historic archive.
Thanks Steve for your website. Trying looking up, "Chimalpahin codex"
Here is another interesting website that contains things from the Aztec and Colonial Era:
http://publications.newberry.org/aztecs/section_4_home.html