I’ll call Sam Milligan and see if he can put a post up about this. But I think if you are referring to the advent of lever harps in the 20th century(as I think you are) I think the earliest version was on Clark Irish harps, which were made in Syracuse New York in the 1920’s. Where Clark got the idea I don’t know.
The earliest modern lever harp was produced by Lyon & Healy starting in the 1950’s when Sam Pratt was head of the harp division. He was also responsible for the style 30, or Princess Louise, which originally had a square back on it. Anyway, Sam Pratt named the Lyon & Healy lever harp the Troubadour, and then, since there was absolutely no music available specifically for it, asked Sam Milligan to produce a book of tunes for it. That book was Fun From the First.