Here are some links that you may find helpful:
I have bought TRRS cables from Amazon (red, black). I can confirm that they work fine.
Drop has an Amazon store. I bought an MT3 /dev/tty ortholinear keycap set from there when they were out of stock on Drop.
I have used Drop + MiTo XDA Canvas keycaps. I liked them.
I have also used YMDK Moon Landing XDA keycaps, which are a clone of GMK Godspeed in XDA profile.
I have always bought DSA keycaps from Pimp My Keyboard. They are a little pricey, but they are good quality, and you have a variety of colors to choose from. This comment has some colorway examples.
Pimp My Keyboard also sells SA keycaps.