In this section, you can download for FREE, ESRI format Shapefiles (*.shp) from Mexico in WGS84 Datum. You just may quote that downloading like this:

"Shape downloaded from http://www.efrainmaps.es. Carlos Efraín Porto Tapiquén. Geografía, SIG y Cartografía Digital. Valencia, Spain, 2020."

However, you can quote the shape as a single (when you download the shape and unzip, please read the file "README)

                                   Shapefile with theContours

                                   of Mexico (in English).

                                   Download in this link: Mexico Contours