Guess I had it coming.
I realized I had the materials to make my own keyboard ribbon cable to replace the broken one that came with this A2S1 keyboard. No problem - followed the wiring schematics I had.. etc. But, alas, didn't work. So I switched back to the cable from my II+ and to my horror, none of the keys were working except Ctrl-Reset.
After a bit of playing around and reading schematics, I ended up replacing the 7400 and 7404 nearest the keyboard cable socket. I managed to restore 60% or so functionality.. most keys working but some producing wrong characters. Then I made a fatal mistake - I did the piggyback test (which had helped me nail down the 7400) on the 555 nearby.. and boom. Back to where I was. Now nothing except CTRL-RESET works. Compounding my error, I went to replace the 555 with another of a bunch I had kicking around.. and the pad around two of the chip legs simply fell off! So now I'm not sure if my 555 is a problem, or if it's not getting proper contact. Doing continuity testing. But for all I know, the keyboard controller could have blown.
Anyway, have learned an expensive lesson I guess. Question is -- what are my odds of finding a replacement A2S1 keyboard PCB if all else fails?