Roland makes a pitch-to-MIDI converter that will probably work with single note harp. I haven't yet tried it, but it's on my list of "wants".
For chorded harp, we'd probably need something along the lines of the guitar synths, where each string is processed separately. Of course, we'd need each hole separately. I think the action will work out to be different from "normal" harp, but that's true of anything of this sort.
-- IronMan Mike Curtis New Cassette available - email for details