A font like Arial Unicode MS has some 150+ accented Greek vowels, including probably all varieties with iota subscriptum. I think it is included in up-to-date Windows versions. Code 2000 is another one, with a more "Times" look.
http://www.earlychristianwritings.com/unicode.html offers free Code 2000 and free TITUS Cyberbit Basic. TCB hides some extra obscure combination towards the end, in the "Private area". And you'll get Armenian, Georgian, Ogham, Runes, both Kana, Arabic with supplements for Pashto and Uyghur, ...
Arial Unicode is 22.7 MB (yes, all CJK stuff you can think of, like the Japanese Industrial Standard symbol, postal marks including the face variety, ...), Code 2000 is 7 MB; TCB
just 1.8 MB...