LEDs have a tendency of "evolving" over time. Different manufacturing processes and manufacturers, etc. Then there are the chemical compositions which have an effect on the color, longevity, and so on.
The chances of finding exact replacements for virtually any LED you have had in use for years is pretty slim, as even the exact LED will have different functional properties when new. The best analog I can think of is trying to perfectly match paint for a large door ding on a car that's been sitting in the direct sun for 5 years. It's probably not going to happen. At minimum, replacement of all the LEDs of the same color on a panel, will have the best chances of getting them to blend back in, as they would be uniform.
All of that said, the LEDs we used in those earlier buttons are the standard 5mm variety, but are rated at a very non-standard 500mw output. Typically, a 500pc minimum order was required for each color, and they are not the typical inexpensive LEDs you see offered everywhere. This is one of the reasons we chose to go a different route with the Helio-style lighting, which uses multiple, more easily-accessible high-output LEDs.
Oh wow ok, yeah I can't find them anywhere; not even on ebay.
Do you still have a few for sale?