Joe, as noted earlier in this thread, luisj40's post at Latarnia covering all of the Santo films is invaluable, and includes Amazon links : here

All but a few are on commercial DVD somewhere, but it's a rat's nest once you realize that there are many reissues and different labels, some of the Mexican DVDs have English subs for the same films released in the US without them, and vice-versa.  Luis did all the work to make it make sense!