Q:   I want to find data for stations at the same elevation. How do I do that?

A:  Elevation is one of the categories under which data can searched.  For example, consider the NOAA/NCDC/DAILY/GLOBALSOD dataset:

 http://ingrid.ldgo.columbia.edu/SOURCES/.NOAA/.NCDC/.DAILY/.GLOBALSOD/

Click on "Searches" to the right of the map.  You will then be able to type in your elevation limits (meters) in the table near the top of the page.