If other internet searchers have landed on this old discussion looking for full Greek diacritic support, there simply isn't any unless it's built into the font itself. By full, I mean you could cleanly (without klugy-looking glyphs) reproduce Smyth's Grammar, including its footnotes, any deep academic discussion, ktl.
That said, actually making a font tailored to your needs is no longer an expensive and difficult proposition. I used Fontographer some 25 years ago, and worked up a very professional-looking font from scratch. There are freeware font editors that will do a decent job, and being mindful of intellectual property rights, you can start off by opening up an existing Greek font and start copying and pasting vowels and adding diacritics (breves, macrons, breve-macrons for that matter) to your heart's content.
Now, this will let you typeset a book or a PDF, but the font has to be either on the end-user's device to go any further than that, and for the PDF, it must be embedded in the document itself.
Keep in mind that although unicode supports a huge number of individual glyphs, there will be a bit of work on your end to actually edit each vowel variation: the combinations possible with iota-subscripts, breves, macrons, diaereses, breathings smooth and rough are simply enormous in number. That said, once you've got a set of several dozen of diacritic combination ornaments, its just a matter of plopping them down upon the vowels, and then a bit of adjusting of each so that each glyph is aesthetically balanced (so a wide macron/breve/breathing/acute combo isn't sticking off to the right of the iota.
But figuring a few hundred combos, it should be doable over a weekend. Possibly you'll want a specialized dead-key keyboard just for that font, in which case I think SIL has a keyboard-making app. You'll probably find making a full dead-key mapping for every glyph unnecessary, and prefer to copy and paste the rarer combinations from a document or floating font-map. My recollection of the SIL app is that it's a big study to figure out just how to do what, but that everything can be done if you fiddle around with it long enough.
Finally, caveat emptor, though this can all be done for free: before doing any hard work of editing all the combinations, make a test-font with dummy-characters simply copied into every slot you plan to for the real ones, and then test the font on a Mac, a Windows machine, a tablet, a PDF, etc. Occasionally fonts go haywire when amateurs don't fully understand how to fix encodings and such. However, even freeware editors have error-checking features that will alert you before you generate your font. Problems will least likely occur if you're simply typesetting a Greek book on your own machine and printer. A large, experienced printing-house will likely be able to deal with your font with little fuss.
If I had it over again, the above procedure would still be preferable to scratching in macrons and such with a fine-point pen.