Hey - welcome to the forum! Happy to have you here.
First and foremost, I think you’d enjoy checking out this thread on various tunings.
In that thread you’ll see links to several different tunings pioneered by Brendan Power, which I’m guessing will be of great interest to you. I know @slim loves the PowerBender and PowerDraw tunings and I’m really looking forward to checking them out! Also in that thread you’ll see a link to the tuning chart on Brendan Power’s website.
The diatonic harmonica was originally tuned so that blowing will always play the I chord, and drawing in the first 5 holes plays the V7 chord.
The concept behind the tuning was to be able to play dance/folk tunes that were popular in the 1800’s in Europe.
The original designers never could have foreseen that the African slaves in America would figure out how to bend notes and that the instrument would evolve into the amazing blues instrument that it has become.
Your post here seems to be looking at the harmonica solely as a chordal instrument, which is only one of its functions, and probably less common than its function as a melodic instrument.
In the Blues, even when the harmonica is functioning as a chordal instrument, it often is just playing single notes, octaves, double-stops, or trills.
In the first half of the 20th century, harmonica groups were a HUGE phenomenon, as I mention in this thread.
They probably reached their height of popularity in Vaudeville in the 20’s and 30’s. In those groups there would typically be (at least) one harmonica covering the bass notes (a bass harmonica) one covering the chord notes (a chordal harmonica) and one for playing the melody, which was typically a chromatic harmonica.
The chordal harps that the players used in those groups were varied, and many of them were almost like wheels with three different harmonicas all attached and they were tuned in various ways. It sounds like one of those instruments may be what you’re interested in checking out.
I don’t know much of anything beyond regular 10-hole diatonic harmonicas, and all of Lee Oskar’s alternate tunings which you can check out in this vid.
OK, hope that helps!
Aloha,
Luke