I have been looking for something like this for a while but hadn't thought of this. It's called bell wire and I found it on a rare trip to home-depot. It's basically one copper wire inside of very very thin insulation. It's fairly rigid but also thin. It's great for doing multi-emitter or anything where you want the resistance of a heavy gauge wire but don't have the room for it. It was cheap too ($7) and it really does work well for a number of mods. It's not the easiest stuff to work with for all mods though because it's ridged but actually for the multi-emitter stuff in particular it's perfect. Anything where you don't have the room it can work.
Another common place for single strand wire is low voltage sprinkler wire that comes in multi conductor cables. 1’ of cable can yield 5’–7’ of conductor.