I've found my MP610's service manuals on Rapidshare. But isn't posting this stuff illegal? I've seen ebook sites selling these things for Canon, for about $15.
I would think selling them would be more illegal than just getting them free. I dont think the manufactures wants anyone to have the service manuals except for repair centers.
To download the manual you could try a Google search on "canon ix4000 service manual" The link to gzhengwei.com including Chinese lettering works from the Google search, but something goes wrong with copy and paste.
Edit2: The gzhengwei link does work, but is extremely slow, so have patience.
Update: The links no longer work. See post #182 for a working link, or use this link: https://yadi.sk/i/xA6212UjXAE98 This link still works Nov. 24th 2017.