I've just used the USGS server to get 1 arc-second DEMS for Mexico. These work (with some reregistration), but I'd like at least 1/3 arc-second.
I just need fairly small areas-- like a 24k quad-worth.
Have you folks ever tried the commercially-available DEMs? I'm guessing they are pricey. Examples:
http://www.landinfo.com/products_dems.htm
Here's their cost:
http://www.landinfo.com/mexstate.htm
There may not be any more detailed data available.
Consider:
The scale of the standard topo for the US is 1:24,000. USGS first produced 1 arc-sec gridded elevation data from these and more recently using more refined algorithms produced 1/3 arc-sec NED. Since Mexico's (and Canada's) standard topo scale is 1:50,000, 1 arc-sec is a sensible limit on what could be produced.
Check with the Mexican government to see if anything more detailed is available.
In areas that overlap with the US, the usgs will supply 1/3 arc-second. Some of these seem to be interpolations on much of the Mexican side, but others do have the detail one expects for 1/3 arc-second (based on comparisons with the GE images.
I used to work for a company that occasionally would contact finer detail satellite (LiDAR) from commercial vendors... back in the days when cost was not an issue. ;^)
USGS has some 1/9 arc-sec LIDAR available which extends about two miles into Mexico.
http://ned.usgs.gov/usgs_gn_ned_dsi/viewer.htm