Unicode 3.1, released in March 2001, included 3 scripts not currently part of OS X. Here is the status of their usability on the Mac as far as I know. Where there is a font but no keyboards, characters can of course still be entered directly using the Character Palette.
Fonts: ALPHABETUM Unicode, Cardo, Code2001, MPH 2B Damase
Fonts: ALPHABETUM Unicode, Cardo, Code2001, MPH 2B Damase, Vulcanius
Fonts: Code2001, MPH 2B Damase, Apple Symbols