Rapid Electronics do fairly small reels of hook up flex that come in various colours , it's plastic but doesn't shrink back when soldered like the old fashioned 50's pvc wiring, I used it on a 30's radio a couple of years back. I think it's sold as a cheaper alternative to silicone test lead wire. It's not as 'limp' as silicone or rubber.
https://www.rapidonline.com/rapid-gw...ck-25m-01-0605