You can make one of these easily with a pair of Lee Oskar harps. I think the bottom (draw) plate is a standard Richter diatonic plate. I think you replace the top (blow) plate with a top plate from a Melody Maker. Is this right? Is it a MM?
What are the two Lee Oskar reed plates used?
blow reeds from "G" MM (top plate, drilled-through holes) draw reeds from "C" Richter (bottom plate, threaded holes) (because Lee Oskar labels the MM's in cross-harp key...)