[DaleHCook]

I have found that 20 gauge wire with 600V rated insulation is next to impossible to find - for some reason.

I suspect it is because electronic equipment nowadays seldom has voltages that high, and if it does it doesn't need anything that large. None of the solid state radio transmitters that I work on have anything over 300 volts. They use combined power MOSFETs in class E mode in their power amps. I do carry some 600 volt wire in the Explorer, along with red and black 5 kv working voltage (20 kv breakdown) test lead wire for higher voltages in vacuum tube transmitters. I even carry a spool of color TV CRT anode wire for a few transmitters with 15 kv plate supplies (but not a lot of current).

NTE does have 600 volt Teflon insulated wire in all 10 colors in gauges from 18 to 26 in 25' packages and 100' spools. See their site.