There's frame stereo and convergent panoramic stereo.  I doubt that the orbital parameters of the missions are declassified, so you will have to use Geodetic Control Points to control the imagery.  I think low-resolution imagery might be free for general searching for specific areas of interest, but the high-res stuff is for sale only.  It's pretty inexpensive considering what you get for your money, but it's not free.  The KH-4b pan was never calibrated; don't know about the KH-9 pan.  All frame imagery was calibrated, but I don't know if the Stellar Calibration Reports have ever been declassified.

We ordered stereopairs via http://earthexplorer.usgs.gov

During the ordering process you can see if some images for your area of interest are already scanned, which might make the processing faster and cheaper. In any case, the price for three scanned stereopairs was around 245$.

You may like to see the URL  below:

http://gcmd.nasa.gov/records/GCMD_CORONA_SATELLITE_PHOTOS.html

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VJ

http://gcmd.nasa.gov/records/GCMD_CORONA_SATELLITE_PHOTOS.html

The EROS data center in Sioux Falls, South Dakota is the place to select and order stereo KH-4, KH-4b, and KH-9 declassified imagery. It costs $30 per scan, but the high resolution is from panoramic cameras, so it takes four scans to get from horizon to horizon. That's four for the Forward Camera, and that's four for the Aft Camera and you need both to achieve stereo. Some current software like that from Leica can handle Rational Functions which will allow you to compile form lines from stereo panoramic imagery, but it's like pulling teeth - slow and extremely difficult. Tough to do.