After alternating between beating and gingerly pressing on my beige 99/4A's God-awful membrane-switched keyboard to obtain desired results -- a key on-screen with no repeats -- I was finally able to locate the leaf-switched type with real beige keys. This was a Radio Shack special I found on eBay and it cost me around $12 shipped.

Originally, I had all of the right hallmarks if looking at the bottom of the keyboard (note, not by looking through the bottom of the console, as the keyboard bottom was covered by a metal shield):

Now for the "good" keyboard. Yes, this keyboard has the leaf switches, even though a few are severely bent they are still operational. Unfortunately, age and shipping were not friendly to this device. All of the keys were loose upon receipt, and just about every one of the green sliders (the "action" of the key) were cracked or broken. The ALPHA LOCK key assembly, for instance, had to be glued back together entirely.

In the end, even if the keyboard part does not work well or will not hold all of the keys, I at least now have beige square-bottomed keys that can be transplanted over to a surrogate black keyboard.