Project Gutenberg has posted them online.

See them here: McGuffy’s Readers. The PDF files include the pictures. (Please note that these are the versions of McGuffey’s Readers revised in the late 1800s, not the originals. The original 1836 versions are available from many sources in book format.)

McGuffey’s Readers World tells more about these great, old-time books.

See also: McGuffey’s Primer and Readers 1-3 in PDF: Perfect for Producing On-Line Video Lessons.