That is a good question. I do not really know how people found them prior to the Pronto, I assume the high end installers have an IR database somewhere they use to take advantage of them.
If I remember correctly the whole discrete on/off/input codes were generated by figuring out what the pronto hex codes ment. There is a great document by Barry Gordon in the pronto files area that discribes that whole procedure. After the document existed it gave people the ability to experiment and eventually utilities were created that made experimenting even easier.
With some remotes you can get the special IR signals via key combo's. For example my Mitsubishi TV has a mode where you hold the Power and type in 90. Then when you press 1-5 you get discrete codes for jumping directly to inputs 1-5! I am sure that some of the other equipment out there works in a similar manner.
I would say that at this point your best bet is to check the pronto files area and see if discrete codes are availible for your device there. If they are, you can convert from Pronto IR codes into a T2 IR code with a little effort.
