go to #musicdsp on efnet and say " why after 10 years of VST is there no harmonizer plug? Get to work peckers!!!!"
to which they will say " pipelineaudio, quit changing your name, and let me get back to working on my l33t ubersynth"
best I can do lately is run a pitch shifter then thru autotune to force it in key
or yamah's Pitchfix VST, which can accidentally harmonize with sometimes nearly sort of kinda ok results