I'm surprised nobody brought up Unicomp. They still make the model M's (with USB interface) and either now hold the patent or under license. Pretty sure it passed to LexMark from IBM and then to Unicomp.
Some claim that the Unicomps don't match the orginal model M's, but they seem the same to me. I know that *very* early Model Ms had capacitive (or Hall Effect?) switches rather dome switches, but it's unlikely many who have used Model Ms over the years have ever used one of those let alone can tell the difference, as that was only for the first couple of years after the introduction of the IBM PC.
(The key to the Model M is not the switch mechanism itself, but the "buckling spring" that provides it's unique feel. You get a "click" before the key bottoms-out. When you hear and feel that click, it is certain that the key has registered, and you train yourself to release pressure. Thus, you do not bottom-out the keys.)
The buckling-spring mechansim simply operates the same type of dome switch used in almost all modern keyboards - albiet a very reliable one.
I have two Unicomp keyboards (I had a second one for work, until Sony made me take it back home due to complaints from the next cube over...) one full-size, and one compact with a pointer stick. (I have to point-out that the pointer stick is *not* the excellent IBM design used on the old ThinkPads. The Unicomp pointer stick is practically worthless, but it is handy to have both that and mouse buttons on the keyboard. I've often used this keyboard as a spare for bootup, as I run my keyboard/mouse on my Linux machine, and use Synergy2 to provide keyboard/mouse access to my Mac Mini. Think I'm going to switch that around the other way and put the keyboard/mouse on the Mini. The reason it is the way it is is becuase traditionally, Synergy did not support Mac as a "server" for keyboard/mouse.)
Anyway, I just discovered that Unicomp sells an 18-key Mac keycap set for $19:
http://pckeyboard.com/page/Buttons/MAC
I beleive these *should* also work on legacy Model Ms. There are some restrictions as to which Unicomp models these will fit.
They've also recently introducted the SpaceSaver-M, designed specifically for Macs:
http://pckeyboard.com/page/SpacesaverM/UNIZPHA
Dunno if this is simply a Spacesaver with the Apple keycaps, or if it is also reprogrammed for the different key positions. I would assume the latter, since Unicomp can provide keyboards with custom programming.
There's also a black version, but it's so ugly I refuse to provide a link.
