This is entirely out of my realm of experience (both playing harmonica, and the 2-card shadow system), but here’s a random combination of ideas in case it sparks something for someone. Here’s how I would begin approaching this:
From my brief google search, I understand that harmonicas can have different numbers of holes. 10, 16, and 24. Personally, I would use my existing number system for these. In my case, that’s the shaper system. After all, it’s just a number that I’m trying to remember, and I already have practice with this system.
If i had a 10-hole harmonica, I might expand my number system to help spread out the repetition of images. I have images for 0-9 and 00-99, so I could intermix 0-9 and 00-09 . There is a possibility to use 0-9 for drawn notes and 00-09 for blown. I’m not sure if that’s beneficial or not, because…
I would use an idea from what I understand of the 2-card shadow system. I would use the loci to indicate if it’s a blown or drawn note. ie: each starting point would be a blown note. Then, add drawn notes on top of that. The next blown note would be the first note at the next loci. This might mean there are more loci (5 for 9 notes in the first line of the example song) instead of stacking them and having 1 loci for all 9 notes.
To indicate bends, I think that I would create a character and/or action that would be interacting with the character representing the note. If there is a difference in bending a blown vs a drawn note, I might create two characters to represent those.
Let’s see if I can re-write the example above in a memory journey. I’ll use a bear as my “bend” character.
Generally, when building a memory palace I try to have the location coordinate with the subject. So for Autumn Leaves I would probably find a walking trail set among the trees and have different trees/etc as loci.
Loci 1: -3 (a butterfly)
Loci 2: -4 4 (two pirate sailboats battling it out, having a cannon battle)
Loci 3: -6 3 (combination lock attached to a butterfly)
Loci 4: -3 (butterfly)
Loci 5: -4 6 6 (sailboat that is dragging two combination locks that are anchors)
THE FALL-ING LEAVES OF RED AND GOLD
Loci 6: -2 3 3 (pirate hook swiping at a butterfly and missing, then swiping at another one and missing)
Loci 7: -5 2* (unicycle is caught by a giant hook, but then a bear breaks the hook)
Loci 8: -2 *3 4 (pirate hook has a butterfly land on it but the butterfly turns into a bear. I drop the hook and jump onto my ship to escape)
I hope some bit of that is helpful!