There is no source for these that I know off.
Look at the back of the switch the cable sheld slides into a fitting, the cable goes through and is fitted with a small swedged fitting on the end, the knob can be turned a bit to show the opening where the swedged fiting can be lifted out, cut it off and remove all.
Get an old time choke cable, the one with the stiff wire cable, from AutoZone or other likely store, cut the pull end off so you only have cable and sheld. Insert cable into the switch and bend a very small loop on the end to hold it, slide cable sheld over the cable.
Fit for length and so forth, dought if you will need a six footer.
Oh yea, take the electrical switch apart and clean well.