I've implemented a patch which will create these keys for linux, but they still need to be implemented on other platforms. The names are as follows.
kbBacktick, kbMinus, kbEqual, kbBracketLeft, kbBracketRight, kbBackslash, kbSemicolon, kbApostrophe, kbComma, kbPeriod, kbSlash
Like all other Gosu keyboard constants, they map to the positions of those keys on the QWERTY keyboard.
Hm. It would be nice to have these, especially since brackets and such are pretty common shortcut keys for scrolling through things like weapons (or tiles, in a map editor). @jlnr is there any reason they were left out in the first place?
Before KbA-KbZ were introduced, Gosu only had constants for keys that are the same all around the world (shift, space, ctrl...)
KbA-KbZ have established that the QWERTY keyboard is what counts as far as Kb* constants are concerned, so there is no reason not to merge this.
I've added constants with these names on all operating systems, but I have only tested Linux and Windows in VMware.