As I mentioned earlier, I buy all mine on e-bay.
Their is one on there right now . Just type in Mopar speaker harness as your search words.
It's a 5 speaker, but the fader switch is not included .
It's sitting about $ 20 with 6 days to go.
Their is a knob style 2 pot stereo fader (nos) listed by another seller correct for 68 B . The E body knob is available in reproduction , if the shafts are the same, there you go.
To find this kind of stuff just type in Mopar speaker as your search words. You will have to weed through about 300 items.If you don't see what you need today , just wait a few days .
Greg