Free map images can be downloaded from these sites.
Note: For unregistered users: You will need to use the Trial version to use these maps, the unregistered Shareware Demo version cannot be used with these images. (The Trial version is included in the OziExplorer Software download.) These maps will require calibrating within OziExplorer using the Load and Calibrate option. (This is described in the Tutorial which can be accessed from the OziExplorer Help Menu).
Free maps and listing of other maps available.
Other Sources
http://www.ofps.ucar.edu/name/science_planning/MX_maps/mx_map.html
Instituto Nacional de Estadística, Geografía e Informática (INEGI)
Bicimapas - About Mexican Topo Maps (for information about INEGI maps)